Mastering Chemistry

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Mastering Chemistry• Book 1B• Topic 2 Microscropic

World I


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ContentUnit 9 Relating the properties of substances to structures and bonding

9.1 Why do different substances have different properties?

9.2 Giant ionic structures 9.3 Properties of ionic compounds

9.6 Applications of graphite

9.4 Giant covalent structures 9.5 Properties of substances with giant

covalent structures

9.7 Simple molecular structures


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ContentUnit 9 Relating the properties of substances to structures and bonding

Key termsSummaryUnit ExerciseTopic Exercise

9.10 Properties of metals

9.8 Properties of substances with simple molecular structures

9.9 Giant metallic structures

9.11 Relationship between structures and physical properties of substances

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Unit 9 Relating the properties of substances to structures and bonding

w The properties of a substance can be determined by its structure.

w Consider these substances:- sodium chloride;- quartz;- iodine; and- copper.

w For example, copper conducts electricity in solid state, but the others do not. The melting point of iodine is low while those of the others are high. This is because the four substances have different structures. Comparing the properties of

substances with different structures

9.1 Why do different substances have different properties? (p.142)

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9.2 Giant ionic structures (p.143)w Sodium chloride, an ionic compound, consists of sodium ions

and chloride ions packed together in a regular arrangement called a lattice.

w A tiny part of the structure is shown below. Billions of sodium ions and chloride ions are arranged in this way to make up a giant ionic structure (巨型離子結構).

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9.2 Giant ionic structures (p.143)w Ionic bonding (electrostatic forces of attraction between

oppositely charged ions) extends throughout the whole structure.

w In the structure, each sodium ion is surrounded by 6 chloride ions and each chloride ion is surrounded by 6 sodium ions.

w The ions in sodium chloride are arranged in a cubic pattern, so sodium chloride crystals are cubic in shape.

Sodium chloride crystals

Giant ionic structure─ sodium chloride Ref.

link/u9_ani01.exe

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9.2 Giant ionic structures (p.143)w Not all ionic compounds form the same structure.

w In the structure of caesium chloride (CsCl), the caesium ions form a cubic arrangement with the chloride ions sitting at the centres of the cubes. Each chloride ion is surrounded by 8 caesium ions while each caesium ion is also surrounded by 8 chloride ions

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9.3 Properties of ionic compounds (p.145)w The table lists the physical properties of some ionic compounds.

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9.3 Properties of ionic compounds (p.145)w Ionic compounds

- are hard but brittle; - have high melting points and boiling points; - are usually soluble in water; - conduct electricity when molten or dissolved in water.

w The properties of ionic compounds reflect their structures as well as their bonding.

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9.3 Properties of ionic compounds (p.145)Hardness and brittlenessw Ionic compounds are hard because the relative motion of the

ions is restricted by the strong ionic bonds between the ions. w Ionic compounds are brittle. When an external force is applied,

- the layers of ions may move relative to each other; - ions of the same charge get close to each other;- repulsion between the ions results and the lattice splits.

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9.3 Properties of ionic compounds (p.145)Melting point and boiling pointw There are strong ionic bonds between the ions with opposite

charges.

w In order to melt and boil ionic compounds, lots of the strong ionic bonds between the ions have to be overcome. This takes a lot of heat, so ionic compounds have high melting points and boiling points.

w All ionic compounds are crystalline solids at room temperature and pressure.

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9.3 Properties of ionic compounds (p.145)Solubilityw In order for a substance to dissolve in a solvent, the following

two conditions must be met:- the attractive forces between its particles and the solvent

particles are strong enough to overcome the attractive forces between particles in the pure substance;

- particles in the substance must separate from each other and become surrounded by the solvent particles.

w Most ionic compounds are soluble in water. Some ionic compounds (e.g. calcium carbonate) are insoluble in water because the ionic bonding within the lattice is stronger than the attraction between the ions and the water molecules.

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9.3 Properties of ionic compounds (p.145)w The process of dissolving sodium chloride in water:

Dissolving sodium chloride (NaCl) in water Ref.

link/u9_ani02.exe

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9.3 Properties of ionic compounds (p.145)w Ionic compounds are usually insoluble in non-aqueous

solvents (非水溶劑), such as cyclohexane (C6H12). w It is because the ionic bonding within the lattice is stronger

than the attraction between the ions and the solvent molecules. The solvent molecules cannot pull the ions out of the lattice.

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9.3 Properties of ionic compounds (p.145)Electrical conductivityw Two conditions must be met for a substance to conduct

electricity: - it must contain charged particles;- these particles must be mobile (可自由流動的).

w Ionic compounds do not conduct electricity in solid state as the ions are in fixed positions and are not free to move around.

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9.3 Properties of ionic compounds (p.145)w When an ionic compound is melted, the ions are able to move

freely throughout the liquid. When electricity is passed through the molten compound, - cations move towards a negative electrode;- anions move towards a positive electrode;- conduction of electricity becomes possible.

w Most ionic compounds are soluble in water. Aqueous solutions of ionic compounds can conduct electricity because - the ions are free to move around in aqueous solutions.

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9.3 Properties of ionic compounds (p.145)w Electrical conductivity of an ionic compound, NaCl:

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9.3 Properties of ionic compounds (p.145)Practice 9.1Caesium is a Group I metal in the Periodic Table. It combines with iodine to form caesium iodide. Ionic bonding exists in caesium iodide.

a) Draw the electron diagram of caesium iodide, showing electrons in the outermost shells only.

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9.3 Properties of ionic compounds (p.145)b) Electrolysis is an experiment which you can perform using an aqueous

solution of caesium iodide to provide evidence for the presence of ionic bonding. i) Draw a labelled diagram of the set-up that you can use for this

experiment.

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9.3 Properties of ionic compounds (p.145)ii) Suggest how your result can show that the bonding is ionic.

iii) Discuss, with explanation, the electrical conductivity of caesium iodide with reference to the type and property of particles in it.

The light bulb lights up.

Caesium iodide does not conduct electricity in solid state as the ions are in fixed positions and are not free to move around.

Caesium iodide can conduct electricity when molten or dissolved in water because the ions are free to move around in molten caesiumiodide or caesium iodide aqueous solution.

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9.4 Giant covalent structures (p.150)w Atoms can join together by covalent bonding to make simple

molecules.w Atoms can also be joined by covalent bonding to form a giant

covalent structure (巨型共價結構). w This type of structure is shown by some elements, such as

silicon and carbon (in the forms of diamond (鑽石) and graphite (石墨)). Some compounds (e.g. silicon dioxide) also have such structure.

w Diamond and graphite are different forms of carbon. Different forms of the same element are called allotropes (同素異形體).

Allotropes are two forms of the same element in which the atoms or molecules are arranged in different ways.

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9.4 Giant covalent structures (p.150)

w In diamond, each carbon atom is covalently bonded to four neighbouring carbon atoms. All the carbon atoms are arranged tetrahedrally.

Carbon in the form of diamond

w The strong covalent bonds extend in all directions throughout the structure.

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w In graphite, carbon atoms are - arranged in flat layers (billions of carbon atoms in each); - arranged in hexagons (1 carbon connected to 3 other); - covalently bonded in a layer, giving a giant covalent structure.

Carbon in the form of graphite

w Only weak van der Waals’ forces (范德華力) exist between the layers of carbon atoms.

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9.4 Giant covalent structures (p.150)w With three covalent bonds formed between carbon atoms

within the layers, an unbonded outermost shell electron is present on each atom.

w These unbonded electrons become delocalised along the layers of carbon atoms.

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w Quartz (石英) is a mineral that contains mainly silicon dioxide. It is the second most abundant mineral in the Earth’s crust.

Silicon dioxide

- a structure similar to that of diamond;- 1 Si bonded to 4 O; 1 O bonded to only 2 Si;- Si and O are held together by strong covalent bonds;- Si : O = 1 : 2, with the chemical formula SiO2.

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9.5 Properties of substances with giant covalent structures (p.152)

w The table lists some properties of diamond, graphite and quartz.

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w Giant covalent substances- are very hard (except graphite); - have high melting points; - are insoluble in water or non-aqueous solvents; - do not conduct electricity (except graphite).

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w In giant covalent substances, strong covalent bonding extends throughout the structure. Relative motion of the atoms is restricted. This makes the substances very hard and useful as abrasives.

Hardness

w For example, sand paper is coated with grains of quartz. Diamond is the hardest substance known. It is used for cutting and grinding hard materials such as glass and stone.

A diamond-studded cutting head used in mining

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w In order to melt a giant covalent substance, - a lot of heat is needed to break lots of strong covalent bonds; - thus these substances have high melting points.

Melting point

w Giant covalent substances are neither soluble in water nor in non-aqueous solvents. - Attraction between their atoms and solvent molecules is not strong enough to overcome the strong covalent bonds that hold the atoms together.

Solubility

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w In most giant covalent substances, - all the outermost shell electrons are either held by individual atoms or used to form covalent bonds;

- there are no mobile electrons or ions;- thus these substances do not conduct electricity (except graphite).

Electrical conductivity

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9.6 Applications of graphite (p.154)

As a lubricant

w Graphite has- van der Waals’ forces between layers;- delocalised electrons along layers.

w The properties of graphite determine its uses.

w Graphite can be used as a solid lubricant (潤滑劑) since the layers of carbon atoms can slide past each other easily.

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9.6 Applications of graphite (p.154)Pencil ‘leads’w Graphite (mixed with clay) is used in pencil ‘leads’. As you

move a pencil across a piece of paper, layers of carbon atoms flake off the structure, so pencil marks appear on the paper.

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9.6 Applications of graphite (p.154)Electrical conductivityw The presence of delocalised electrons along the layers allows

graphite to conduct electricity (along a layer but not across layers) when a voltage is applied.

w Graphite is used to make brushes in electric motors and electrodes in dry cells

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9.6 Applications of graphite (p.154)Practice 9.2The structures of silicon and silicon dioxide are shown below.

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9.6 Applications of graphite (p.154)Explain why a) silicon has a high melting point;

b) silicon dioxide can be used as an abrasive.

In order to melt silicon with a giant covalent structure, lots of strong covalent bonds between atoms have to be broken. A lot of heat is needed. Thus, silicon has a high melting point.

Due to the strong covalent bonds in silicon dioxide, relative motion of the atoms is restricted. Thus, the oxide is hard and strong.

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9.7 Simple molecular structures (p.156)w In most non-metals, atoms are joined together to form small

molecules. Examples include

- nitrogen (N2) in Group V; - oxygen (O2) in Group VI; and - the halogens in Group VII, which are all diatomic.

w Compounds of most non-metals also have simple molecular structures (簡單分子結構). Examples include

- ammonia (NH3); - water (H2O); and - carbon dioxide (CO2).

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9.7 Simple molecular structures (p.156)w Simple molecular substances have strong covalent bonds

joining their atoms within each molecule.

w Only weak attractive forces exist among the molecules.

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9.7 Simple molecular structures (p.156)

w Iodine is a black crystalline solid. It contains a regular arrangement of iodine molecules held closely together by weak van der Waals’ forces.

Structure of iodine

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w Under room conditions, carbon dioxide is a gas.

Structure of dry ice

w At temperatures below –78.5 °C, carbon dioxide gas changes to a solid (dry ice) directly without going through the liquid state.

w In each carbon dioxide molecule, strong covalent bonds hold the carbon atom and oxygen atoms together.

w Dry ice contains a regular arrangement of carbon dioxide molecules held closely together by weak van der Waals’ forces.

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9.8 Properties of substances with simple molecular structures (p.158)

w The table lists the properties of some simple molecular substances.

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w Simple molecular substances- are soft if they are solids; - have low melting points and boiling points; - are often slightly soluble or even insoluble in water but soluble in non-aqueous solvents;

- do not conduct electricity.

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w Simple molecular solids are usually soft - due to the weak attractive forces (i.e. van der Waals’ forces) among the molecules;

- it is easy to break the solids.

Hardness

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w Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules. Thus, simple molecular substances have low melting points and boiling points.

Melting point and boiling point

w This explains why- simple molecular substances are liquids or gas (at r.t.);- many of the liquids are volatile (揮發性)。

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w The van der Waals’ forces among iodine moleculesare so weak that iodine changes directly from solid to vapour(i.e. it sublimes) on gentle warming.

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w Simple molecular substances are usually soluble in non-aqueous solvents, but slightly soluble or even insoluble in water.

Solubility

w Iodine is very soluble in cyclohexane (C6H12), a non-aqueous solvent, but only slightly soluble in water

Iodine is added to cyclohexane (left) and water (right)

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w Iodine + cyclohexane- attractive forces exist between molecules of the two substances;- attractive forces are much the same as that in the pure substances;- mix together easily

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w Iodine + water- little interaction between molecules of iodine and water;- attractive forces among water molecules are strong;- attractive forces between iodine molecules and water molecules are

weak in comparison;- iodine molecules and water molecules do not mix easily.

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w Simple molecular substances do not contain mobile ions or delocalised electrons, so they cannot conduct electricity.


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Q (Example 9.1)Neon and oxygen are elements in the same period of the Periodic Table.

a) Draw electron diagrams for molecules of neon and oxygen respectively, showing electrons in all shells.

b) Name the attractive forces that exist among oxygen molecules. c) The boiling points of neon and oxygen are listed below.

Explain why the boiling point of oxygen is higher than that of neon.

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a)

A

b) Van der Waals’ forces c) Neon exists as monatomic molecules while oxygen exists as diatomic

molecules. An oxygen molecule has a larger size than a neon molecule. Thus, stronger van der Waals' forces exist among oxygen molecules.

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Practice 9.3Solid silicon dioxide (SiO2) melts at 1 710 °C while solid silicon tetrachloride (SiCl4) melts at –70 °C. Neither of the liquids formed conducts electricity.

a) i) Draw the electron diagram of silicon tetrachloride, showing electrons in the outermost shells only.

ii) What type of structure does silicon tetrachloride have? Simple molecular structure

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b) Explain the difference in melting points of the two compounds.

c) Explain why neither of the liquids of the two compounds conducts electricity.

Silicon dioxide has a giant covalent structure. Lots of strong covalent bonds between atoms have to be broken in melting. Silicon tetrachloride has a simple molecular structure. Weak attractive forces exist among the molecules. The covalent bonds in silicon dioxide are much stronger than the attractive forces among silicon tetrachloride molecules. Thus, silicon dioxide has a higher melting point than silicon tetrachloride.

Liquids of the two compounds do not contain mobile ions or delocalisedelectrons.

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9.9 Giant metallic structures (p.162)w Metals form giant metallic structures (巨型金屬結構) in

which a regular three-dimensional arrangement of positive metal ions is surrounded by a ‘sea’ of delocalised electrons. The metal ions are packed closely together.

The structure of metals Ref.

link/t3_u11_ani_01e.exe

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9.10 Properties of metals (p.163)w The table lists the properties of some metals.

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9.10 Properties of metals (p.163)

w Most metals- have high densities; - have high melting points and boiling points; - are good conductors of electricity and heat; - are malleable (i.e. can be hammered into shapes); - are ductile (i.e. can be drawn into wires).

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w Metals usually have high densities because the positive metal ions are very closely packed in the structures of metals.

Density

The density of gold is 19.3 g cm-3

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w In a piece of metal, there are strong attractive forces between their positive metal ions and the ‘sea’ of delocalised electrons.

Melting point

w To melt the metal, a lot of heat is needed to overcome the attractive forces. Hence metals usually have high melting points. Metals, apart from mercury, are solids at room temperature and pressure.

The melting point of gold is 1 064 oC

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w Metals conduct electricity due to the delocalised electrons within their structures.


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w When a piece of metal is heated, - the kinetic energy of electrons in the structure increases; - delocalised electrons in the heated region move around faster and conduct the heat rapidly to other parts.

Heat conductivity

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w When you apply a force to a piece of metal, - layers of metal ions slide over each other to new positions;- delocalised electrons are free to move in the structure; - ions still held in their new positions by the ‘sea’ of electrons; - the metal now has a different shape (malleable and ductile).

Mealleability and ductility

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9.11 Relationship between structures and physical properties of substances (p.166)

w You should be able to deduce the physical properties of substances from their structures and bonding, and vice versa.

Deducing the structures of substances from their properties

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Q (Example 9.2)Consider the experimental set-up shown below.

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In the above experiment, the bulb lights up when solid strontium bromide becomes molten.

a) Strontium (Sr) is a Group Il element below calcium in the Periodic Table. It combines with bromine to form strontium bromide. i) Draw the electron diagram of strontium bromide, showing electrons in

the outermost shells only. ii) What type of structure does strontium bromide have?

b) i) Explain why the bulb lights up when solid strontium bromide becomes molten.

ii) State and explain the observation at the carbon electrode X.

c) Explain why solid strontium bromide is brittle.

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a) i)ii) Strontium bromide has a giant ionic structure.

b) i) Strontium bromide conducts electricity in molten state because the ions are free to move..

ii) A reddish brown gas is observed. Negative bromide ions are attracted to the positive electrode X. At this electrode, these ions lose electrons to become atoms. The atoms then join in pairs to form molecules. 2Br- à Br2 + 2e-

c) In strontium bromide, the ions are held together by strong ionic bonds. When a force is applied, the layers of ions may move relative to each other. This can bring ions of the same charge close to each other, resulting in repulsion. Thus, the lattice splits.

A

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Q (Example 9.3)Explain why quartz (SiO2) is harder than dry ice (CO2).

Quartz has a giant covalent structure. Strong covalent bonding extends throughout the structure. Relative motion of the atoms is restricted. This makes quartz very hard.

Dry ice consists of discrete carbon dioxide molecules. The molecules are held together by weak van der Waals' forces. Relative motion of the molecules is easy when a force is applied. Hence dry ice is less hard compared with quartz.

A

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Practice 9.41 Copper(II) chloride, carbon (in the form of diamond), iodine and copper

have different properties. These differences are the results of different types of structure and different forces or bonds between the particles in the structures.

Complete the table below.

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Copper(II) chloride

Carbon (diamond) Iodine Copper

Structure

Particles

Forces or bond

m. p.

Forces or bond overcome on melting

Solubility in water


giant ionic

oppositely charged ions

ionic bonds

high

ionic bonds

soluble

good conductor when molten or dissolved in water

giant covalent

atoms

covalent bonds

very high

covalent bonds

insoluble

non-conductor

simple molecular

small moleculescovalent bonds between atoms in molecule;van der Waals’ forces among molecules

low

van der Waals’ forces

slightly soluble

non-conductor

giant metallicpositive metal ions in sea of delocalised e-

metallic bonds

high

metallic bonds

insoluble

good conductor

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2 Study the properties of four substances (W, X, Y and Z) listed in the table below. Decide the type of structure that is likely to be present in each substance.

W has a giant metallic structure. X has a simple molecular structure. Y has a giant covalent structure. Z has a giant ionic structure.


71Unit 9 Relating the properties of substances to structures and bonding

Key terms (p.170)giant ionic structure 巨型離子結構 van der Waals’

forces范德華力

non-aqueous solvent 非水溶劑 quartz 石英

mobile 可自由流動的 lubricant 潤滑劑

giant covalentstructure

巨型共價結構 simple molecular structure

簡單分子結構

diamond 鑽石 volatile 揮發性

graphite 石墨 giant metallic structure

巨型金屬結構

allotrope 同素異形體



Summary (p.171)

1 The following table summarises the properties of substances with the four types of structures: giant ionic, giant covalent, simple molecular and giant metallic.



Summary (p.171)



Summary (p.171)

2 Allotropes are two or more forms of the same element inwhich the atoms or molecules are arranged in different ways.

3 a) In graphite, only weak van der Waals’ forces exist between the layers of carbon atoms.

b) Graphite can be used as a solid lubricant as the layers of carbon atoms can slide past each other easily.

c) The presence of delocalised electrons along the layers allows graphite to conduct electricity when a voltage is applied.



Summary (p.171)

4 The flow diagram below shows how to determine the structure and bonding in a substance based on some of its physical properties.



Unit Exercise (p.173)78

Note: Questions are rated according to ascending level of difficulty (from 1 to 5):

question targeted at level 3 and above; question targeted at level 4 and above;

question targeted at level 5. ‘ * ’ indicates 1 mark is given for effective communication.




1 Complete the following concept map.PART I KNOWLEDGE AND UNDERSTANDING



Unit Exercise (p.173)80(a) metallic

(b) ionic (c) covalent (d) metallic (e) high (f) solid (g) molten (h) ionic (i) high (j) molten

(k) dissolved in water (l) simple molecular (m) low (n) non-conductors (o) van der Waals’ forces (p) covalent (q) high (r) non-conductors




2 Which of the following diagrams shows the giant ionic structure of sodium chloride?

Answer: D

PART II MULTIPLE CHOICE QUESTIONS




3 Which of the following compounds has a giant ionic structure? A N2O4B HNO3C NCl3D NH4NO3

(HKDSE, Paper 1A, 2014, 2)

Answer: D




4 Which of the following is the worst conductor of electricity?

A Mg(s) B SiCl4(l) C MgCl2(l) D C(graphite,s)

Answer: B

Explanation: SiCl4 has a simple molecular structure.




5 Which of the following correctly describes the ability of potassium bromide to conduct electricity?

Solid Molten potassium potassium Potassium bromide bromide bromide in water

A does not does not conducts conduct conduct

B does not conducts conducts conduct

C conducts does not does not conduct conduct

D conducts conducts does not conduct

Answer: B




6 Which of the following combinations about the structure and bonding of silicon dioxide is correct?

Structure Bonding A Silicon dioxide has Each oxygen atom

a simple molecular is covalently bonded structure. to two silicon atoms.

B Silicon dioxide has Each oxygen atom a giant covalent is covalently bonded structure. to two silicon atoms.

C Silicon dioxide has Each silicon atom a simple molecular is covalently bonded structure. to two oxygen atoms.

D Silicon dioxide has Each silicon atom a giant covalent is covalently bonded structure. to two oxygen atoms.

Answer: B




7 Which of the following statements describes the attractive forces between molecules (intermolecular forces)?

A They are strong covalent bonds which hold molecules together.B They are strong ionic bonds which hold molecules together.C They are weak forces formed between covalently bonded molecules.D They are weak forces which hold ions together in a lattice.

(Cambridge IGCSE, Paper 2, 0620/23, Jun. 2016, 6)

Answer: C




8 Silicon carbide has a structure similar to that of diamond. It has a high melting point because

A the silicon-carbon covalent bonds are strong. B the attractive forces between silicon carbide molecules are strong. C the attractive forces between silicon ions and carbide ions are strong. D the silicon carbide molecules have a tetrahedral shape.

Answer: A




9 Neon exists as a gas at room temperature and pressure because A neon is chemically inert. B neon molecules are monoatomic. C the attractive force between neon atoms is weak. D the outermost electron shell of a neon atom has an octet structure.


Answer: C




10 Which of the following describes the appearance of iodine under the stated conditions?

Solid Dissolved in cyclohexane A purple bluish black B brown bluish black C shiny black purple D shiny black brown

Answer: C




11 Solid X has a high melting point, does not conduct electricity as a solid, but does when it is dissolved in water. What might solid X be?

A Calcium chloride B Hydrogen chloride C Silver D Silicon

Answer: A

Explanation: X has a giant ionic structure.




12 The structures of diamond and graphite are shown.

Which statement about diamond and graphite is INCORRECT? A Diamond is used in cutting tools because the strong covalent bonds

make it very hard. B Graphite acts as a lubricant because of the weak forces between the

layers. C Graphite conducts electricity because the electrons between the layers

are free to move. D Graphite has a low melting point because of the weak forces between the

layers. (Cambridge IGCSE, Paper 1, 0620/13, Jun. 2016, 4)

Answer: D

diamond graphite




13 Which of the following substances is hard, with a high melting point and does NOT conduct electricity in any physical state?

A Silicon dioxide B Magnesium C Copper(II) chloride D Lead(II) bromide

Answer: A

Explanation:Silicon dioxide has a giant covalent structure




14 Which of the following exists as discrete molecules?

A AluminiumB Graphite C Oxygen D Silicon

Answer: C




Directions: Questions 15–17 refer to some physical properties of four substances W, X, Y and Z listed below.




Answer: D

15 Which of the substances could be mercury?

A W B X C Y D Z

Explanation:Z is a liquid at room temperature. It has a giant metallic structure as it conducts electricity both as solid and as liquid.




Answer: A

16 Which of the substances could be silicon dioxide?

A W B X C Y D Z

Explanation:Silicon dioxide has a giant covalent structure. It has high melting and boiling points. It does not conduct electricity.




Answer: B

17 Which of the substances could be hydrogen bromide?

A W B X C Y D Z

Explanation:Hydrogen bromide has a simple molecular structure. It has low melting and boiling points. It does not conduct electricity.




18 The diagram shows the set-up of an experiment:

Which of the following methods may light up the light bulb? (1) Heating the sodium bromide powder until molten (2) Adding deionised water to the sodium bromide powder (3) Replacing the sodium bromide powder with bromine liquid

A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3)

(HKDSE, Paper 1A, 2014, 20) Answer: A




19 A substance has a high melting point and conducts electricity in solid state. It may be

(1) an element with simple molecules. (2) an element with giant metallic structure. (3) a compound with giant ionic structure.

A (1) only B (2) only C (1) and (3) only D (2) and (3) only

(HKDSE, Paper 1A, 2014, 20) Answer: B

Explanation:(3) A compound with giant ionic structure does NOT conduct electricity in solid state.




20 Complete the table to show the bonding and structure for each of the three elements in the third period of the Periodic Table.

PART III STRUCTURED QUESTIONS

Element Magnesium Silicon ChlorineBonding

Structure

metallic bonding

giant metallic structure

covalent bonding

giant covalent structure

covalent bonds join the atoms within the molecules; van der Waals’ forces exist among molecules

simple molecular structure

(3)

(3)




21 Argon and chlorine are elements in the same period of the Periodic Table. a) Draw the electron diagram for a molecule of argon, showing electrons in

all shells. b) What is the type of intermolecular force in chlorine gas?

(HKDSE, Paper 1B, 2015, 1(a)–(b))

Answers for the questions of the public examinations in Hong Kong are not provided (if applicable).




22 Complete the table below for properties of compounds of some Period 3 elements.

Compound of sodium and

oxygen

Compound of phosphorus and

chlorineCompound of

sulphur and oxygen

Formula of compound

State at room temperature and pressure

liquid gas

Type of structure

Na2O

solid

giant ionic structure

PCl3


SO2


(3)

(1)

(3)




23 Explain the following in terms of the structure and bonding of the substances being heated.

a) When a few iodine crystals are gently warmed, a purple vapour is observed.

b) When a few potassium chloride crystals are gently warmed, no change is observed. Very strong and prolonged heating is required to melt the crystals.

c) Very strong heating fails to melt a sample of silicon dioxide.

Iodine has a simple molecular structure. (1) There are only weak van der Waals’ forces among iodine molecules so the force of attraction is easily overcome by gentle heating, allowing I2 molecules to escape from its lattice. (1)

Potassium chloride has a giant ionic structure. (1) There are strong ionic bonds between the ions with opposite charges. It takes a lot of heat to separate the ions in melting. (1)

Silicon dioxide has a giant covalent structure. (1) Lots of strong covalent bonds between atoms have to be broken in melting. A lot of heat is needed. (1)




24 Aluminium fluoride and silicon tetrachloride differ markedly in their melting points.

Deduce the type of bonding present in each of these compounds, and draw an electron diagram to illustrate the bonding and structure of each compound.

Ionic bonding is present in aluminiumfluoride. (1)

Covalent bonding is present in silicon tetrachloride. (1)

(1) (1)




25 Both caesium (Cs) and sodium (Na) are elements in Group I of the Periodic Table. Caesium reacts with chlorine to form caesium chloride.

a) Solid caesium chloride has a giant ionic structure. i) Draw a diagram to show the structure of caesium chloride. ii) Explain why solid caesium chloride is brittle.

b) Predict, with ONE reason, whether sodium or caesium is more reactive towards chlorine.

(HKDSE, Paper 1B, 2013, 8(b)–(c))





26 The table shows the melting points of the elements in Period 3 of the Periodic Table.




a) State the type of structure and bonding in each of the following elements: i) Aluminiumii) Silicon iii) Sulphur




b) i) Draw electron diagrams for molecules of chlorine and argon respectively, showing electrons in outermost shells only.

ii) Name the attractive forces that exist among chlorine molecules.

iii) Explain why the melting point of chlorine is higher than that of argon. Van der Waals’ forces (1)

Argon exists as monatomic molecules while chlorine exists as diatomic molecules. A chlorine molecule has a larger size than an argon molecule. (1) Thus, stronger van der Waals’ forces exist among chlorine molecules. (1)




27 Magnesium oxide is a compound formed by the reaction of magnesium with oxygen. The table below lists the melting points of these three substances.




In terms of structure and bonding, explain why a) magnesium oxide has a very high melting point;

b) oxygen has a very low melting point;

c) magnesium has a high melting point.

Magnesium oxide has a giant ionic structure. (1) There are strong ionic bonds between the ions with opposite charges. Lots of the strong ionic bonds between the ions have to be overcome in melting. This takes a lot of heat. (1)

Oxygen has a simple molecular structure. (1) Weak attractive force exist among oxygen molecules. Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules in melting. (1)

Magnesium has a giant metallic structure. In magnesium, there are strong attractive forces between the positive metal ions and the ‘sea’ of delocalised electrons. A lot of heat is needed to overcome the attractive forces in melting. (1)




28 This question is about three substances: copper, sodium chloride and water. a) Complete the table below to show some properties of the three

substances.

yes (1)

yes yes (2)

no (1)




b) Explain whether solid copper conducts electricity.

c) Explain whether solid sodium chloride is brittle.

d) Explain why liquid water does NOT conduct electricity.

Solid copper conducts electricity due to the mobile delocalised electrons in the structure. (1)

Solid sodium chloride is brittle. Sodium chloride forms a lattice of alternating positive and negative ions. The ions are held by strong ionic bonds. (1) When an external force is applied, the layers of ions may move relative to each other. This can bring ions of the same charge close to each other and result in repulsion between the ions. As a result, the lattice splits. (1)

Liquid water has NO mobile electrons or ions. (1)




29 The graph shows the variation in melting temperatures of the elements across Period 3 (Na to Ar) of the Periodic Table.




a) i) Describe, with the aid of a labelled diagram, the structure and bonding in aluminium.

ii) Hence explain why aluminium has a high melting point.

Aluminium has a giant metallic structure. (1) It contains a regular three-dimensional arrangement of positive aluminium ions surrounded by a ‘sea’ of delocalised electrons. (1) The strong electrostatic forces of attraction between positive aluminium ions and delocalisedelectrons make up the metallic bond. (1) Diagram showing a regular arrangement of aluminium ions in a ‘sea’ of delocalised electrons (1)

A lot of heat is needed to overcome the strong attractive forces between the positive aluminiumions and the ‘sea’ of delocalised electrons in melting. (1)




b) Silicon has a giant covalent structure. Explain how this structure results in the high melting point shown on the graph.

c) Explain why chlorine has low melting point and boiling point.

Silicon has a giant covalent structure.Lots of strong covalent bonds between atoms have to be broken in melting.A lot of heat is needed. (1)

Chlorine has a simple molecular structure. (1) Weak attractive forces exist among chlorine molecules. Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules in melting and boiling. (1)




30 Silicon reacts with chlorine to form a low boiling point chloride. a) Draw the electron diagram for the chloride,

showing electrons in the outermost shells only.

b) Silicon reacts with oxygen to form a high melting point oxide. Suggest why the oxide has a high melting point whereas the chloride has a low boiling point. Silicon dioxide has a giant covalent structure. (1)

Lots of strong covalent bonds between atoms have to be broken in melting. A lot of heat is needed. Thus, silicon dioxide has a high melting point. (1) Silicon tetrachloride has a simple molecular structure. (1) Weak attractive forces exist among silicon tetrachloride molecules. Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules in boiling. Thus, silicon tetrachloride has a low boiling point. (1)




31 Most solids exist as lattice structures. a) Complete the table, using a tick (✓) if the substance conducts electricity

or a cross (✗) if the substance does not conduct electricity.

b) Explain the electrical conductivities of sodium and of sodium oxide in the solid and liquid states. (Edexcel Advanced Subsidiary GCE, Unit 1, 6CH01/01R, Jun. 2013, 22(d)(i)–(ii))

Sodium conducts electricity in the solid and liquid states due to the mobile delocalised electrons in the structure. (1) Sodium oxide in solid state does not conduct electricity as the ions are in fixed positions and are not free to move around. (1) Sodium oxide in liquid state can conduct electricity because the ions are free to move around in the liquid. (1)

✓ ✓ (1)

✗ ✓ (1)




32 The structures of diamond and graphite are shown.

diamond graphite




a) Explain how the structure of diamond relates to its use in cutting hard materials.

b) Graphite is quite soft and is used in pencils. Explain how its use in pencils depends on its structure.

c) Explain why graphite conducts electricity while diamond does not.

Diamond has a giant covalent structure. (1) In diamond, strong covalent bonding extends throughout the structure. Relative motion of the atoms is restricted. This makes diamond very hard. (1)

In graphite, weak van der Waals’ forces exist between the layers of carbon atoms. (1) When a pencil is moved across a piece of paper, layers of carbon atoms flake off graphite easily, so pencil marks appear on the paper. (1)

The presence of mobile delocalised electrons along the layers of carbon atoms in graphite allows graphite to conduct electricity. Diamond has NO mobile electrons or ions. (1)




33 The table below shows some properties of three elements in the Periodic Table.

a) Describe how the information in the table shows that silicon is difficult to classify as a metal or a non-metal.

b) Explain why aluminium is a good conductor of electricity.

c) Explain why silicon has a high melting point.

Difficult to classify because it has metallic and non-metallic properties. i.e. it has a high melting point like a metal but is brittle like a non-metal. (1)

Due to the mobile delocalised electrons in aluminium. (1)

Silicon has a giant covalent structure. (1) Lots of strong covalent bonds between atoms have to be broken in melting. A lot of heat is needed. (1)




34 The structure of solid lead(II) bromide and liquid bromine are shown below.




a) Bromine exists as diatomic molecules. Draw the electron diagram for a bromine molecule, showing electrons in the outermost shells only.

*b) Describe the structures and bonding of these two substances and the differences in • their volatility; • their electrical conductivity.

Lead(II) bromide has a giant ionic structure. (1) There are strong ionic bonds between the ions with opposite charges in lead(II) bromide. Hence lead(II) bromide is non-volatile. (1) Lead(II) bromide does not conduct electricity in solid state, but conducts electricity when molten or dissolved in water. (1) Bromine has a simple molecular structure. (1) Weak attractive forces exist among the molecules. Hence bromine is volatile. (1) Bromine does not conduct electricity. (1) Communication mark (1)




*35 Carbon dioxide and silicon dioxide are compounds that occur naturally on Earth. The table shows some information about the two compounds.




Use ideas about structure and bonding to explain the similarities and differences between the properties of carbon dioxide and silicon dioxide.

(OCR GCSE 21st Century Science (Higher Tier), Chem. A, A172/02, Jun. 2013, 5(a))




Similarities and differences in properties• Both have similar chemical formula. (1) • Both do not conduct electricity. (1) • Carbon dioxide has a low melting point / boiling point while silicon dioxide has a high melting point / boiling point. (1)

• At room temperature, carbon dioxide is a gas while silicon dioxide is a solid. (1)

Structure and bonding • The bonding in both is covalent. (1) • Each silicon atom is bonded to four oxygen atoms in silicon dioxide. (1) • Each carbon is bonded to two oxygen atoms in carbon dioxide. (1) • Carbon dioxide has a simple molecular structure. (1) • Silicon dioxide has a giant covalent structure. (1) • Both have NO mobile electrons or ions. Hence both do not conduct electricity. (1) • The weak attractive forces among carbon dioxide molecules do NOT require a lot of

heat to overcome. (1) • The strong covalent bonds between atoms in silicon dioxide require a lot of heat to

break. (1) Communication mark (1)




36 In 2009 a new material called graphane was discovered. The diagram shows part of a model of the structure of graphane. Each carbon atom is bonded to three other carbon atoms and to one hydrogen atom.

a) Deduce the type of crystal structure shown by graphane.

b) State how two carbon atoms form a carbon-carbon bond in graphane.

c) Suggest why graphane does NOT conduct electricity. (AQA Advanced Subsidiary GCE, Unit 1, Jun. 2013, 3(a)–(c))

Giant covalent structure (1)

Share a pair of electrons. / One electron from each carbon atom. (1)

NO mobile electrons or ions (1)




37 This question is about two compounds formed from phosphorus. a) Phosphorus combines with magnesium to form magnesium

phosphide. i) Draw the electron diagram for magnesium phosphide, showing

electrons in the outermost shells only.




ii) Give the chemical formula of magnesium phosphide.

iii) Explain whether or not you would expect magnesium phosphide to have a high melting point.

Mg3P2 (1)

Magnesium phosphide has a high melting point. Magnesium phosphide has a giant ionic structure. (1)

There are strong ionic bonds between the ions with opposite charges. Lots of the strong ionic bonds between the ions have to be overcome in melting. This takes a lot of heat, so magnesium phosphide has a high melting point. (1)




b) Phosphorus combines with hydrogen to form phosphine. i) Draw the electron diagram for phosphine, showing electrons in the

outermost shells only.




ii) Give the chemical formula of phosphine.

iii) Explain whether or not you would expect phosphine to have a high water solubility.

PH3 (1)

Phosphine is slightly soluble / insoluble in water. (1) When phosphine is added to water, there is little interaction between molecules of phosphine and water. (1) The attractive forces among water molecules are strong. The attractive forces between phosphine molecules and water molecules are weaker in comparison. (1) Thus, water molecules tend to stick together, rather than allowing phosphine molecules to come between them. As a result, phosphine molecules and water molecules do not mix easily. (1)




38 Explain each of the following: a) The boiling temperature of chlorine is –34 °C, but temperatures above

1 027 °C are needed to obtain chlorine atoms from chlorine molecules.

b) Solid iodine is very soluble in cyclohexane, a non-aqueous solvent.

Chlorine has a simple molecular structure. (1) Weak attractive forces exist among chlorine molecules. Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules in boiling. (1) To obtain chlorine atoms from chlorine molecules, the strong covalent bonds between chlorine atoms have to be broken. A lot of heat is needed. (1)

When iodine is added to cyclohexane, attractive forces exist between molecules of iodine and cyclohexane. These attractive forces are much the same as that in the pure substances. (1) Thus, iodine molecules and cyclohexane molecules mix together easily. (1)




c) Graphite conducts electricity.

d) Bromine is less volatile than chlorine.

Graphite contains mobile delocalised electrons along the layers of carbon atoms. (1)

A bromine molecule has a larger size than a chlorine molecule. (1) Thus, stronger van der Waals’ forces exist among bromine molecules. Hence bromine is less volatile than chlorine. (1)




39 There are three types of giant structures – ionic, metallic and giant covalent. a) In an ionic compound, the ions are held in a lattice by strong forces.

i) Explain the term ‘lattice’.

ii) Explain how the ions are held together by strong forces.

b) Describe the bonding in a typical metal.

Ions packed together in a regular arrangement. (1)

Electrostatic forces of attraction / attraction between opposite charges (1)

Strong electrostatic forces of attraction between positive metal ions and delocalised electrons. (1)




c) The electrical conductivities of the three types of giant structures are given in the following table.

Explain the differences in electrical conductivity between the three types of giant structure and the difference, if any, between the solid and liquid states of the same structure.

(Cambridge IGCSE, Paper 3, 0620/31, Jun. 2013, 8)




A substance with a giant ionic structure does not conduct electricity in solid state as the ions are in fixed positions and are not free to move around. (1)

The substance can conduct electricity in liquid state because the ions are free to move around in the liquid. (1)

A substance with a giant metallic structure conducts electricity in solid and liquid states due to the mobile delocalised electrons in the structure. (1)

A substance with a giant covalent structure does not conduct electricity in solid and liquid states because it has NO mobile electrons or ions. (1)




40 Read this passage about metals. Elements are divided into metals and non-metals. All metals are electrical conductors. Many of them have high densities and they are usually ductile and malleable. These properties influence how the metals are used. a) Explain the meaning of the terms ‘ductile’ and ‘malleable’.

*b) By considering their structures, explain why metals are ductile and malleable.

ductile — can be drawn into a wire (1) malleable — can be hammered into shape (1)

A metal contains a regular three-dimensional arrangement of positive metal ions surrounded by a ‘sea’ of delocalised electrons. (1) When a force is applied to a piece of metal, the layers of metal ions slide over each other to new positions. The delocalised electrons are free to move in the structure, but the ions are still held together in their new positions by the ‘sea’ of electrons. The metal has a different shape. (1) Communication mark (1)




c) Copper is ductile. How is this property useful in everyday life?

d) Name ONE metal that has a low density.

e) Choose another physical property of metals, and give ONE example of how it is useful.

Making copper electric wires (1)

Any Group I metals (1)

Any one of the following: • Good conductor of heat (1) To make cooking pans. (1) • Shiny appearance (1) To make jewellery. (1)



Topic Exercise (p.185)138

Note: Questions are rated according to ascending level of difficulty (from 1 to 5):

question targeted at level 3 and above; question targeted at level 4 and above;

question targeted at level 5. ‘ * ’ indicates 1 mark is given for effective communication.




1 A sample of gallium has two isotopes, 69Ga and 71Ga. The graph below shows the relative abundance of the isotopes.

What is the relative atomic mass of this sample of gallium? A 69.4 B 69.6 C 69.8 D 70.0

PART I MULTIPLE CHOICE QUESTIONS

Answer: C




2 Which of the following atoms has the smallest number of neutrons?

A 63Cu B 59Co C 58Ni D 57Fe


Answer: C




3 Which of the following ions contains the fewest number of electrons?

A NH4+

B P3–

C Ca2+

D Cl–Answer: A




4 !"#$Sc forms a cation carrying a charge of +3. How many electrons and neutrons are there in the cation?

Number of electrons Number of neutrons A 18 21 B 18 24 C 21 24 D 21 21

Answer: B




5 Which of the following statements about nitrogen, oxygen, fluorine and neon is correct?

A They can form anions. B They contain diatomic molecules. C They have multiple covalent bonds between atoms. D They are gases at room temperature and pressure.

Answer: D

Explanation:Option A — Neon does not form anions. Option B — Neon contains monatomic molecules.




6 Both radium (Ra) and calcium (Ca) belong to the same group of the Periodic Table. Which of the following statements is INCORRECT?

A Radium is a good conductor of electricity in the solid state. B Radium atoms readily donate electrons to form Ra2+ ions. C Both radium and calcium become tarnished after exposed to air for

some time. D Radium is less reactive than calcium.


Answer: D




Directions: Questions 7 and 8 refer to the following outline of the Periodic Table. The letters A, B, C and D are NOT the symbols of the elements.

7 Which of the letters represents a metal with a high melting point and boiling point?

8 Which of the letters represents an element which does NOT form compounds?

Answer: C

Answer: A




9 The diagram shows elements W, X, Y and Z in a section of the Periodic Table.

Which statements about the reactivity of the elements is correct? A X is more reactive than Y, and W is more reactive than Z. B X is more reactive than Y, and Z is more reactive than W. C Y is more reactive than X, and W is more reactive than Z. D Y is more reactive than X, and Z is more reactive than W.

(Cambridge IGCSE, Paper 1, 0620/12, Nov. 2015, 22)

Answer: C

Explanation:The reactivity of Group I elements increases going down the group. Thus, Y is more reactive than X. The reactivity of Group VII elements decreases going down the group. Thus, W is more reactive than Z.




10 Elements X and Y form an ionic compound with chemical formula X2Y. If the ion of X and the ion of Y have the same electronic arrangement, which of the following may this compound be?

A Lithium oxide B Aluminium oxide C Potassium sulphideD Magnesium chloride


Answer: C




11 Element Q belongs to Group II of the Periodic Table. It combines with element R to give an ionic compound with chemical formula Q3R2. Which group of the Periodic Table does R belong to?

A Group III B Group V C Group VI D Group VII


Answer: B




12 Silicon is an element in Group IV of the Periodic Table. The oxide of silicon has the chemical formula SiO2. Which of the following statements about silicon and its oxide is correct?

A Silicon is a good conductor of heat. B Silicon exists as simple molecules. C SiO2 is a hard material at room temperature. D SiO2 dissolves in water to give an acidic solution.


Answer: B




13 What is the charge on the nickel ion in Ni3(PO4)2?

A +2 B +3 C –2 D –3 Answer: A




14 A spot of blue solution was placed in the centre of a piece of moist filter paper supported on a microscope slide and the following experiment was carried out.

After some time, a blue colour moved towards the negative terminal, but no change was visible in the region of the positive terminal. This is because

A the negative ions in the solution were colourless and the positive ions were blue. B the positive ions in the solution were colourless and the negative ions were blue. C the negative ions in the solution had not moved but the positive ions had moved. D the positive ions in the solution had not moved but the negative ions had moved.

(Edexcel Advanced Subsidiary GCE, Unit 1, 6CH01/01R, Jun. 2014, 10)

Answer: A

Explanation:The blue positive ions moved towards the negative terminal.




15 Quartz (SiO2) is harder than dry ice (CO2) because

A the atomic size of silicon is larger than that of carbon. B a silicon atom has more electrons than a carbon atom has. C quartz has a giant network structure, but dry ice consists of discrete

molecules. D the silicon-oxygen bond in quartz is strong, but the carbon-oxygen

bond in dry ice is weak. (HKDSE, Paper 1A, 2018, 5)

Answer: C




16 Consider the following information concerning metal Y: (1) Y reacts vigorously with water. (2) Y forms an oxide with chemical formula Y2O. (3) An atom of Y has five occupied electron shells.

Y may be A silver (Ag). B caesium (Cs). C strontium (Sr). D rubidium (Rb).


Answer: D




17 The table below shows some properties of potassium.

Rubidium is below potassium in Group I of the Periodic Table. What are the properties of rubidium?

(1) Its melting point is above 63 °C. (2) It is very soft. (3) It reacts explosively with water.


Answer: C

Explanation: (1) The melting points of Group I elements decrease going down the group. Thus, the melting point of rubidium is lower than that of potassium.




18 Astatine (At) is a halogen with an atomic number of 85. Which of the following statements about astatine is / are correct?

(1) Astatine exists as diatomic molecules. (2) Astatine is more reactive than fluorine. (3) The compound formed between hydrogen and astatine has a

very high boiling point.

A (1) only B (2) only C (1) and (3) only D (2) and (3) only

Answer: A

Explanation: (2) The reactivity of halogens decreases going down the group. Thus, astatine is less reactive than fluorine. (3) Hydrogen and astatine form a covalent compound with a simple molecular structure, i.e. a compound with a lower boiling point.




19 Which of the following statements concerning helium is / are correct? (1) Helium is chemically inert. (2) Helium exists as diatomic molecules. (3) The outermost electron shell of a helium atom has an octet

structure. A (1) only B (2) only C (1) and (3) only D (2) and (3) only

(HKDSE, Paper 1A, 2017, 16) Answer: A




20 A substance has a high melting point and can conduct electricity when molten. It may be

(1) aluminium. (2) sulphur. (3) magnesium chloride.

A (1) only B (2) only C (1) and (3) only D (2) and (3) only Answer: C

Explanation: (1) Aluminium conducts electricity when in solid and molten states. (2) Sulphur does not conduct electricity. (3) Magnesium chloride does not conduct electricity in the solid state. However, it conducts electricity when molten.




21 What types of bonding are present in ammonium carbonate? (1) Covalent (2) Dative covalent (3) Ionic


Answer: D




Directions : Each question (Questions 22–25) consists of two separate statements. Decide whether each of the two statements is true or false; if both are true, then decide whether or not the second statement is a correct explanation of the first statement. Then select one option from A to D according to the following table :

A Both statements are true and the 2nd statement is a correct explanation of the 1st statement.

B Both statements are true but the 2nd statement is NOT a correct explanation of the 1st statement.

C The 1st statement is false but the 2nd statement is true.D Both statements are false.




1st statement

22 A sulphide ion contains one more occupied electron shell than a sulphur atom.

Answer: CExplanation: The electronic arrangement of a sulphide

ion is 2,8,8 while that of a sulphur atom is 2,8,6. A sulphide ion and a sulphur atom have the same number of occupied electron shells.

2nd statement

A sulphur atom gains electrons to form a sulphide ion.

23 The melting point of silicon is higher than that of that in an aluminium atom.

The number of electrons in a silicon atom is greater than aluminium.

(HKDSE, Paper 1A, 2015, 35) 24 Bromine is a good conductor of

electricity.Molecules in bromine are mobile.

Answer: B

Answer: C

25 Potassium sulphate is a covalent compound.

Potassium sulphate can conduct electricity when dissolved in water. Answer: C




PART II STRUCTURED QUESTIONS26 Explain whether BaCl2 or OCl2 would have a higher melting point.

(HKDSE, Paper 1B, 2018, 3(a))





27 Lithium occurs naturally in two isotopes, 6Li and 7Li. It can form lithium nitride (Li3N) when burnt in air. a) Calculate the percentage abundance of 6Li in nature.

(Relative atomic mass: Li = 6.9) b) Draw the electron diagram for lithium nitride, showing electrons in the

outermost shells only. (HKDSE, Paper 1B, 2018, 1(a))





28 The set-up of an experiment for studying the movement of ions is shown below.Describe and explain what you would expect to observe when the circuit is closed for a period of time.

A pink colour appears near electrode X (1) as positive cobalt(II) ions are attracted towards the negative electrode / electrode X. (1)

A yellow colour appears near electrode Y (1) as negative chromate ions are attracted towards the positive electrode / electrode Y. (1)




29 Rubidium, Rb, is a Group I element. It has similar physical and chemical properties to the other elements in Group I. a) Predict how many electrons there are in the outermost shell of a

rubidium atom. b) Predict ONE physical property of rubidium which is the same as that of

a transition metal such as copper.

c) Predict TWO physical properties of rubidium which are different to those of a transition metal such as copper.

1 (1)

Any one of the following: • Conductor of electricity / heat (1) • Malleable (1) • Ductile (1) • Shiny (1)

Any two of the following: • Low melting point / boiling point (1) • Soft / rubidium can be cut easily (1) • Low density (1)




d) Give a reason why Group I metals are usually stored in oil.

e) The following diagram shows the reaction between a Group I metal and water. Although the metal reacts vigorously with the water, gas G does not ignite spontaneously.

i) Name metal A.

ii) Write a word equation for the reaction involved.

To stop them from reacting with air / water vapour / moisture. (1)

Lithium / sodium (1)

lithium + water à lithium hydroxide + hydrogen (1) or sodium + water à sodium hydroxide + hydrogen (1)




30) The electronic arrangements of atoms of five elements, A, B, C, D and E are given below. These letters are NOT chemical symbols.




Choose letters from the table to answer parts (a) and (b). Each letter may be used once, more than once or not at all. a) Give the letters of the TWO elements which belong to the same period of

the Periodic Table. Give a reason for your answer.

b) Give the letters of the TWO elements which belong to the same group of the Periodic Table. Give a reason for your answer.

c) Elements B and D combine to form a compound. i) Draw the electron diagram for the compound, showing electrons in the


ii) Name the compound.

B and C (1) Their atoms have the same number of / two occupied electron shells. (1)

C and D (1) Their atoms have the same number of / six outermost shell electrons. (1)

Carbon disulphide (1)

or (1)




d) Elements D and E combine to form a compound. i) Draw the electron diagram for the compound, showing electrons in the


ii) Name the compound. Potassium sulphide (1)

or (1)




31 Calcium can burn in air. Calcium nitride is formed along with calcium oxide. a) Draw the electron diagram of calcium nitride,

showing electrons in the outermost shells only.

b) In terms of charges, explain why the ratio of calcium ions to nitride ions is 3 : 2 in the lattice.

c) Calcium nitride reacts with water to give calcium hydroxide and ammonia: calcium nitride + water à calcium hydroxide + ammonia i) Give the chemical formula of calcium hydroxide. ii) Ammonia is a gas at room temperature and presssure. The boiling

point of liquid ammonia is –34 °C. Explain why liquid ammonia has a low boiling point.

Ca(OH)2 (1)

So that the charges balance / number of positive charges = number of negative charges (1)

Ammonia has a simple molecular structure. (1) Weak attractive forces exist among ammonia molecules. Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules in boiling. Thus, ammonia has a low boiling point. (1)




32 Hydrogen reacts with sodium to form sodium hydride, an ionic compound which has the same structure as sodium chloride. a) Draw the electron diagram of sodium hydride, showing electrons in the


b) Give the chemical formula of sodium hydride.

c) Draw a diagram to show the structure of sodium hydride. NaH (1)




33 Magnesium reacts with oxygen to form magnesium oxide. a) Describe what happens, in terms of electron loss and gain, when

magnesium atoms combine with oxygen atoms.

b) Give the chemical formula of magnesium oxide. c) Magnesium oxide is used to manufacture heat-resistant bricks for

furnace linings in the steel-making industry. State and explain the property of magnesium oxide that makes it suitable for this use.

A magnesium atom needs to lose two electrons (1) while an oxygen atom needs to gain two electrons so as to obtain stable outermost shells of 8 electrons. (1) When magnesium atoms combine with oxygen atoms, two electrons from each magnesium atom are transferred to each oxygen atom. (1)

MgO (1)

High melting point (1) Strong attractive forces between oppositely charged ions / strong ionic bonding (1)




34 Some airbags in cars contain sodium azide (NaN3). a) Sodium azide has a high melting point. Predict the type of bonding in

a crystal of sodium azide. Suggest why its melting point is high.

b) The azide ion has the formula N3–.

i) The azide ion can be represented as N≡N–N–. One of these bonds is a dative covalent bond. On the following diagram, draw an arrowhead on one of the bonds to represent the direction of donation of the lone pair in the dative covalent bond.

N≡N–N–

ii) Give the formula of a molecule that has the same number of electrons as the azide ion.

iii) Which is the correct formula of magnesium azide?Mg3N MgN MgN6 Mg3N2

(AQA Advanced Subsidiary GCE, Unit 1, Jun. 2015, 7(d)–(e))

Ionic bonding (1) There are strong ionic bonds between the ions with opposite charges in sodium azide. Lots of the strong ionic bonds between the ions have to be overcome in melting. This takes a lot of heat, so sodium azide has a high melting point. (1)

CO2 / N2O / BeF2 / HN3 (1) MgN6 (1)

N≡NàN– (1)




35 The table shows the melting points, boiling points and electrical properties of five substances A to E.

Choose a substance from the table above to match each of the following descriptions. A substance may be used once, more than once or not at all. Justify each choice with evidence from the table.




One has been completed as an example. This substance is covalent and is a solid at room temperature (25 °C): DEvidence: Its melting point is above room temperature. It has a low melting point and it does not conduct as a liquid, so it is covalent.

a) This substance has a giant covalent structure: Evidence:

b) This substance is a metal: Evidence:

c) This substance is a liquid at room temperature (25 °C):Evidence:

d) This substance is an ionic solid: Evidence:

E (1) It has a high melting point / a high boiling point. It does not conduct electricity. (1)

B (1) It is a good conductor of electricity when in solid and liquid states. (1)

A (1) Its melting point is below room temperature. Its boiling point is above room temperature. (1)

C (1) It has a high melting point / a high boiling point. It does not conduct electricity when solid and conducts electricity when liquid. (1)




36 a) Chlorine has an atomic number of 17. Chlorine-35 and chlorine-37 are two isotopes of chlorine. Complete the table to show the numbers of protons, neutrons and electrons in each of the isotopes.




b) Tetrachloromethane is a simple molecular, covalent compound. The formula of its molecule is CCl4. Draw an electron diagram to show the bonding in a molecule of tetrachloromethane, CCl4. Show outermost shell electrons only.




*c) The diagrams show the arrangements of carbon atoms in diamond and in graphite.

Compare a use of diamond with a use of graphite, explaining each use in terms of the bonding and structure. In your answer you should use information from the diagrams.

(Edexcel GCSE (Higher Tier), Unit C2, Jun. 2014, 5(a)(i),(b)–(c))




c)Diamond is used in cutting tools because it is very hard. (1) In diamond, each carbon atom bonded to four other carbon atoms. Strong covalent bonding extends throughout the structure. Relative motion of the atom is restricted. (1) Any one use of graphite and explanation • To make electrodes. (1) In graphite, each carbon atom is bonded to three other carbon atoms, and an unbonded outermost shell electron is present on each atom. These unbonded electrons become delocalised along the layers of carbon atoms. These mobile delocalised electrons allow graphite to conduct electricity. (1) • To make lubricant. (1) In graphite, weak van der Waals’ forces exist between the layers of carbon atoms. The layers of carbon atoms can slide past each other easily. (1) • To make pencil ‘leads’. (1) In graphite, weak van der Waals’ forces exist between the layers of carbon atoms. When a pencil is moved across a piece of paper, layers of carbon atoms flake off graphite easily, so pencil marks appear on the paper. (1) Communication mark (1)




37) This question is about Group VII elements. a) Suggest why a fluoride ion (F–) is more stable than a fluorine atom.

b) Chlorine reacts with fluorine to form chlorine monofluoride. Draw the electron diagram of chlorine monofluoride, showing electrons in the outermost shells only.

A fluoride ion has a complete outermost electron shell. (1)




c) Astatine (At) is below iodine in Group VII. i) The table below shows the states of Group VII elements at room

temperature and pressure.

Use this information to deduce the state of astatine at room temperature and pressure.

ii) Astatine reacts with sodium to form a compound. (I) Draw the electron diagram of the compound, showing electrons in the


(II) Name the compound.

Solid (1)

Sodium astatide (1)




38 Diamond and silicon dioxide have similar properties.

a) Describe TWO similarities and ONE difference between the structures of diamond and silicon dioxide.

b) Explain why diamond does not conduct electricity.

c) Explain why silicon dioxide has a high melting point.

diamond silicon dioxide

Similarities: • Atoms in both of them are covalently bonded. (1) • Both have giant structures. (1) One difference from: • Silicon dioxide contains two elements but diamond only contains one (carbon). (1) • All carbon atoms form four bonds in diamond but only silicon atoms form four bonds in silicon dioxide. (1)

Diamond has NO mobile electrons or ions. (1)

Silicon dioxide has a giant covalent structure. (1) Lots of strong covalent bonds between atoms have to be broken in melting. A lot of heat is needed. Thus, silicon dioxide has a high melting point. (1)




39 Refer to the following information of phosphorus and fluorine.




a) State the electronic arrangement of a phosphorus atom. b) All phosphorus atoms have the same atomic number. Explain why some

phosphorus atoms have different mass numbers.

c) Phosphorus and fluorine combine to form a compound. i) Draw the electron diagram for the compound, showing electrons in the


ii) Give the name and chemical formula of the compound.

iii) Calculate the relative molecular mass of the compound. (Edexcel Advanced Subsidiary GCE, Unit 1, Jun. 2012, 26(c))

2,8,5 (1)

Phosphorus exists as isotopes. (1)

Phosphorus trifluoride (1) PF3 (1)

31.0 + 3 x 19.0 = 88.0 (1)




40 The elements potassium and fluroine and the compound potassium fluoride can be used to show the connection between bonding, structure and physical properties. a) i) Describe the structure and bonding in potassium with the help of a

diagram.

ii) Explain why potassium is a good conductor of electricity.

Potassium contains a regular three-dimensional arrangement of positive potassium ions surrounded by a ‘sea’ of delocalised electrons. (1) The strong electrostatic forces of attraction between positive potassium ions and delocalised electrons make up the metallic bond. (1) Diagram showing a regular arrangement of potassium ions in a ‘sea’ of delocalised electrons (1)

Due to the mobile delocalised electrons in potassium. (1)




b) i) Draw the electron diagram of a fluorine molecule, showing electrons in all shells.

ii) Describe the attractive forces within and between the molecules in liquid fluorine. Covalent bond exists within a molecule. (1) Van der Waals’ forces exist among molecules. (1)




c) i) Describe how atoms of potassium and fluorine combine to form potassium fluoride.

ii) Explain why potassium fluoride does NOT conduct electricity until it is heated above its melting point.

A potassium atom needs to lose one electron (1) while a fluorine atom needs to gain one electron so as to obtain stable outermost shells of 8 electrons. (1) When potassium atoms combine with fluorine atoms, one electron from each potassium atom is transferred to each fluorine atom. (1)

Potassium fluoride in solid state does not conduct electricity as the ions are in fixed positions and are not free to move around. (1) Potassium fluoride in molten state can conduct electricity because the ions are free to move around in the liquid. (1)




41 The table below lists some properties of diamond and graphite.




With reference to the bonding and structure, explain why a) diamond and graphite have high melting points;

b) graphite is a good conductor of electricity;

c) diamond is very hard;

d) graphite can be used to make pencil cores for marking on paper.

Both diamond and graphite have a giant covalent structure. (1) Lots of strong covalent bonds between atoms have to be broken in melting. A lot of heat is needed. (1)

Graphite contains mobile delocalised electrons along the layers of carbon atoms. (1)

In diamond, strong covalent bonding extends throughout the structure. Relative motion of the atoms is restricted. (1)

In graphite, weak van der Waals’ forces exist between the layers of carbon atoms. (1) When a pencil is moved across a piece of paper, layers of carbon atoms flake off graphite easily, so pencil marks appear on the paper. (1)




42 Nickel is a metal with a high melting point. a) Explain, in terms of its structure and bonding, why nickel has a high

melting point.

b) Draw a labelled diagram to show the arrangement of particles in a crystal of nickel. In your answer, include at least six particles of each type.

c) Explain why nickel is ductile (can be stretched into wires). (AQA Advanced Subsidiary GCE, Unit 1, Jun. 2014, 3(a)(ii)–(iv))

Nickel contains a regular three-dimensional arrangement of positive nickel ions surrounded by a ‘sea’ of delocalised electrons. (1) A lot of heat is needed to overcome the strong attractive forces between the positive nickel ions and the ‘sea’ of delocalised electrons in melting. (1)

Diagram showing a regular arrangement of nickel ions in a ‘sea’ of delocalised electrons (1)

When a force is applied to a piece of nickel, the layers of nickel ions slide over each other to new positions. The delocalised electrons are free to move in the structure, but the ions are still held together in their new positions by the ‘sea’ of electrons. The metal has a different shape. (1)




43 Aluminium can be extracted from ores such as bauxite. Bauxite is refined to produce aluminium oxide. Electrolysis of molten aluminium oxide produces aluminium and oxygen. a) Give the chemical formula of aluminium oxide.

*b) Describe, with the aid of a labelled diagram, the structure and bonding in aluminium and explain why aluminium is malleable.

Al2O3 (1)

Aluminium contains a regular three-dimensional arrangement of positive aluminium ions surrounded by a ‘sea’ of delocalised electrons. (1) Diagram showing a regular arrangement of aluminium ions in a ‘sea’ of delocalised electrons (1) When a force is applied to a piece of aluminium, the layers of aluminium ions slide over each other to new positions. The delocalised electrons are free to move in the structure, but the ions are still held together in their new positions by the ‘sea’ of electrons. The metal has a different shape. (1) Communication mark (1)




c) Oxygen is a gas at room temperature and has a very low boiling point. i) Draw the electron diagram of an oxygen molecule, showing

electrons in the outermost shells only.

ii) Explain why oxygen has a low boiling point.

d) Explain why ionic compounds, like aluminium oxide, conduct electricity when molten.

Oxygen has a simple molecular structure. (1) Weak attractive forces exist among oxygen molecules. Very little heat is needed to overcome the attractive forces among the molecules and separate the molecules in boiling. Thus, oxygen has a low boiling point. (1)

Molten aluminium oxide contains ions that are free to move around. (1)




44 This question compares sodium iodide and iodine. a) How do sodium iodide and iodine differ in their solubility in water?

Explain your answer. Sodium iodide is soluble in water while iodine is only slightly soluble. The δ– ends of the water molecules attract the positive sodium ions sufficiently to remove them from the lattice. The sodium ions then become surrounded by water molecules. (1) On the other hand, the δ+ ends of the water molecules attract the negative iodide ions sufficiently to remove them from the lattice. The iodide ions then become surrounded by water molecules as well. (1) When iodine is added to water, there is little interaction between molecules of iodine and water. (1) The attractive forces among water molecules are strong. The attractive forces between iodine molecules and water molecules are weaker in comparison. (1) Thus, water molecules tend to stick together, rather than allowing iodine molecules to come between them. As a result, iodine molecules and water molecules do not mix easily. (1)




b) Explain why molten sodium iodide conducts electricity but molten iodine does not.

c) The boiling point of sodium iodide is 1 304 °C while that of iodine is 184 °C. Explain this difference.

Molten sodium iodide contains ions that are free to move around. (1)Molten iodine does not contain mobile ions or delocalised electrons. (1)

Sodium iodide has a giant ionic structure while iodine has a simple molecular structure. (1) The ionic bonds between sodium ions and iodide ions in sodium iodide are much stronger than the attractive forces among iodine molecules. Thus, sodium iodide has a much higher melting point than iodine. (1)




*45 A phosphorus atom can be shown as "$%"P. What can be deduced from this information about the structure of a phosphorus atom and the position of phosphorus in the Periodic Table?

• The atom contains 15 protons. (1) • The atom contains 16 neutrons. (1) • The atom contains 15 electrons. (1) • The electronic arrangement of the atom is 2,8,5. (1) • The atom has three occupied electron shells. (1) • The atom has 5 outermost shell electrons. (1) • The element is in Period 3 of the Periodic Table. (1) • The element is in Group V of the Periodic Table. (1) Communication mark (1)




*46 Bricks made from silicon dioxide are used to line furnaces that operate at high temperatures. Suggest and explain why silicon dioxide is used to make bricks for high-temperature furnaces. Refer to the structure and bonding in silicon dioxide in your answers.

In silicon dioxide, each silicon atom is bonded to four oxygen atoms while each oxygen atom is bonded to only two silicon atoms. Silicon atoms and oxygen atoms in the whole structure are held together by strong covalent bonds. (1) Silicon dioxide has a high melting point. In order to melt silicon dioxide, lots of strong covalent bonds between atoms have to be broken. A lot of heat is needed. Thus, silicon dioxide has a high melting point. (1) Silicon dioxide has a hard structure. In silicon dioxide, strong covalent bonding extends throughout the structure. Relative motion of the atoms is restricted. This makes silicon dioxide very hard. (1) Communication mark (1)


Unit 9 Relating the properties of substances to structures and bonding 196

Topic Exercise (p.185)*47 Explain the increasing order of melting points of the three Period 2

elements below: oxygen < lithium < carbon (graphite) Oxygen has the lowest melting point as it has a simple molecular structure. (1) Very little heat is needed to overcome the weak attractive forces among the molecules and separate the molecules in melting. (1)

Lithium has a giant metallic structure. (1) The attractive forces between the positive lithium ions and the ‘sea’ of delocalisedelectrons are stronger than the attractive forces among oxygen molecules. Thus, the melting point of lithium is higher than that of oxygen. (1)

Graphite has the highest melting point as it has a giant covalent structure. (1)

Lots of strong covalent bonds between atoms have to be broken in melting. A lot of heat is needed. (1)

Communication mark (1)

Mastering Chemistry

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