Properties of MatterChapter 2

Classifying Matter

Physical Properties

Chemical Properties

Pretest

1. What instrument would you use to measure temperature?

2. Which of the following is a unit of volume?a. gramb. atmospherec. meterd. liter

3. What characteristic of matter can you measure using a graduated cylinder?

Pretest (continued)

4. The sides of a cube are 2 cm by 2 cm. What is the volume of the cube?

5. What additional quantity would you need to calculate the density of the cube described in Question 4?

6. Which of the following is NOT studied in chemistry? a. composition of matter b. reactions of substances c. properties of materials d. motion of large objects

In this Section

You will learn:1. Why are elements and compounds defined as

pure substances?2. How do mixtures differ from pure substances?3. What is the main difference among solutions,

suspensions, and colloids?Key terms that you will learn are:

- pure substance - homogeneous mixture- element - solution- atom - suspension- compound - colloid- heterogeneous mixture

Classifying Matter

• Matter is classified based on its composition.

• A sample of matter that can be classified into one of two groups:– Pure substances.

– Mixtures.

Pure Substances• Pure substances always

have the same composition.– Two types of pure

substances:• Elements.• Compounds.

– Every sample in a given substance has the same properties because a substance has a fixed, uniform composition.

Elements

• Element: a pure substance that cannot be broken down into simpler substances.– An atom is the smallest particle

of an element.• There are just over 100 different

types of elements.

– An element has a fixed composition because it is made of only one type of atom.

I (Iodine)

Hg (Mercury)

Au(Gold)

Representing Elements• A chemical symbol is a notation that is made up

of one, two, or three letters that represent an element.• Jons Berzelius (Swedish) first suggested it in 1813.

•The first letter is always a capital letter.•If a second and third letters, if used, is always written in lower case.

–Question: Why is this important?

Co vs. CO

Compounds• Compounds are made up of two

or more simpler substancesthat are chemically combined.– A compound has properties that

are different from the substances that make it up.

– Compounds can be broken down into simpler substances.

– A compound always contains two or more elements joined together in a fixed proportion.

Mixtures• Mixtures are made of two or

more simpler substances that do not chemically combine.– The individual substances in a

mixture retain some of their properties.

– Properties of a mixture are less constant than the properties of a substance.

– The properties of a mixturecan vary because the composition of the mixture is not fixed.

Classifying of Mixtures• Mixtures are classified by

how well the parts are distributed.– Heterogeneous mixtures.

• The parts of the mixture are noticeably different from one another.

– Homogeneous mixtures.• The substances in the mixture

are so evenly distributed it is difficult to distinguish one substance in the mixture from another.

– Appears to contain only one kind of substance.

Particle Size & Mixture Type

• The size of the particles have an effect on the properties of a mixture.

• Based on the size of its largest particlea mixtures can be classified as:– Solution.

– Suspension.

– Colloid.

Solutions

• Solutions are formed when substances dissolve and a homogeneous mixture is formed.– The particles in a solution are very small:– Properties of solutions include:

• Do not settle out of the solution.• Can not be filtered. • Do not scatter light.

– Examples include sugar water & stainless steel (a mixture of iron, chromium, and nickel).

Suspensions

• A suspension is a heterogeneous mixture that separates into layersover time.– The particles in a suspension are large.

– Properties of suspensions include:• Scatter light (cloudy).

• Can be filtered.

– Examples include muddy water and some types of paint.

Colloids

• A colloid is a homogenous mixturethat does not separate into layers.– A colloid contains particles that are

intermediate in size between the small particles in a solution and the large particles in a suspension.

– Properties include:• Cannot be filtered.

• Scatter light (cloudy).

– Examples of colloids include fog and milk.

Solutions, Colloids & Suspensions

• Properties of solutions, colloids and suspensions compared to one another.

Review of Classifying Matter

From this SectionYou have learned:1. Why are elements and compounds defined as

pure substances?2. How do mixtures differ from pure substances?3. What is the main difference among solutions,

suspensions, and colloids?You should be able to define:

- pure substance - homogeneous mixture- element - solution- atom - suspension- compound - colloid- heterogeneous mixture

Section 2.1 Assessment (p.44)

In this SectionYou will learn:1. What are some examples of physical

properties?2. How can knowing the physical properties of

matter be useful?3. What processes are used to separate mixtures?4. When does a physical change occur?Key terms that you will learn are:

- physical property - boiling point- viscosity - filtration- conductivity - distillation- malleability - physical change- melting point

Physical Properties• A physical property is any characteristic of a

material that can be observed or measuredwithout changing the composition of the substances in the material.– Intensive properties do not depend on the amount

of matter present:- Viscosity - Melting Point

- Conductivity - Boiling Point

- Malleability - Density

- Hardness

– Extensive properties depend on the amount of matter present.

- Mass - Volume

- Weight -Length

Viscosity

• Viscosity is a liquids resistance to flow.– The greater the

viscosity the slower the liquid flows.

– Viscosity usually decreases withincreased temperature.

Conductivity

• Conductivity is the ability of a material to allow heat to flow.– Good conductivity = heat flows

easily.– Materials with high

conductivity are called conductors.

• Metals are good conductors.• Materials that are a good

conductor of heat are also usually good conductors of electricity.

Malleability & Brittleness

• Malleability is the ability of a solid to be hammered without shattering. – Most metals are

malleable.

• Brittleness is a property of a solid that causes it to shatter if struck with a hammer.

Hardness

• Hardness refers to how well a solid resists being scratched.– Harder substances will

scratch softer substances.

– Diamonds are the hardest naturally occurring substance.

Melting & Boiling Points

• The melting point is the temperature at which a substance changes from a solid to a liquid.

• The boiling point is the temperature at which a substance will boil.

Density

• Density is the ratio of the mass of a substance to its volume.

Density = Mass/Volume

• Density can be used to test the purity of a substance.– For example the density of silver is

10.5 g/cm3. The density of a quarter is 9.9g/cm3…

• A quarter is not pure silver.

Using Physical Properties

• The physical properties of a substance can be used to identify unknown substances.

• When testing an unknown substanceyou should:– Decide what properties to test.

– Test the unknown sample.

– Compare the results with data reported for known materials.

Density and Unknown Substances

Density can be used to help identify unknown substances.– A person could determine the composition of a piece

of jewelry by comparing its density with the density of a known substance such as silver or gold.

• Gold has a density of 19.3 g/cm3.• 9ct gold has a density of 10.9 to 12.7 g/cm3.• 14ct gold has a density of 12.9 to 14.6 g/cm3.• 18ct yellow gold has a density of 15.2 to 15.9 g/cm3.• 18ct white gold has a density of 14.7 to 16.9 g/cm3.• 22ct gold has a density of 17.7 to 17.8 g/cm3.• Silver has a density of 10.5 g/cm3.• Sterling Silver has a density of 10.2 to 10.3 g/cm3. • Platinum has a density of 21.4 g/cm3.• Palladium has a density of12.0 g/cm3.• Copper has a density of 9.0 g/cm3.

Choosing Materials

• The properties of a substance help to determine which materials are chosen for a specific use.– When choosing materials for a specific

use you should:• Determine what properties the material

needs.– Look at several properties of the

material, not just one, to determine what is needed.

• Choose the material that best fits the needs.

Separating Mixtures

• Properties of a material can be used to separate mixtures.– Filtration: a process that

separates materials based on the size of the particles.

– Distillation: a process that separates the substances in a solution based on their boiling point.

Recognizing Physical Changes

• A physical change occurs when some of the properties of a material change, but the substances in the material remain the same.– A change in appearance, but not

composition.

– Some physical changes can be reversed, others cannot.

From this SectionYou have learned:1. What are some examples of physical

properties?2. How can knowing the physical properties of

matter be useful?3. What processes are used to separate mixtures?4. When does a physical change occur?You should be able to define:

- physical property - boiling point- viscosity - filtration- conductivity - distillation- malleability - physical change- melting point

Section 2.2 Assessment (p.51)

In this SectionYou will learn:1. When can chemical properties be observed?2. What observations might indicate a chemical

change has occurred?3. What is the difference between chemical and

physical changes?Key terms that you will learn are:

- chemical property- flammability- reactivity- chemical change- precipitate

Chemical Properties

• A chemical property of matter is any ability to produce a change in the composition of matter.– Chemical properties can be observed

only when the substances in a sample of matter are changing into different substances.

– Examples of chemical properties include:• Flammability.

• Reactivity.

Flammability & Reactivity• Flammability is a material’s ability to

burn in the presence of oxygen.

• Reactivity is a property that describes how readily a substance combines chemically with other substances.– For example:

• Oxygen will react with most other elements. – Iron is also reactive and will combine with oxygen

to form rust (this process is called oxidation).

• Nitrogen is not very reactive and therefore does not react with most substances.

Recognizing Chemical Reactions• A chemical change occurs

when a substance reacts and forms one or more new substances.

• Three common types of evidence for a chemical change are:– Change in color.– The production of a gas.– The formation of a precipitate.

• A precipitate is a solid that formsand separates from a liquid mixture.

Chemical or Physical Changes

• It is not always easy to distinguish a chemical and physical changes.– Color changes, the production of a gas,

etc…may not be enough evidence that a chemical change has taken place.

• Key evidence is the production of new substances that are different from those present before the change.– When matter undergoes a chemical change,

the composition of matter changes. – When matter undergoes a physical change, the

composition of matter remains the same.

From this SectionYou have learned:1. When can chemical properties be observed?2. What observations might indicate a chemical

change has occurred?3. What is the difference between chemical and

physical changes?You should be able to define:

- chemical property- flammability- reactivity- chemical change- precipitate

Section 2.3 Assessment (p.58)