CHEMICAL BONDS

A link between atoms of two or more

elements by mutual attraction

Electronegativity Difference

• If the difference in electronegativities is between:

– 1.7 to 4.0: Ionic

– 0.3 to 1.7: Polar Covalent

– 0.0 to 0.3: Non-Polar Covalent Example: NaCl

Na = 0.8, Cl = 3.0

Difference is 2.2, so

this is an ionic bond!

IONIC BOND

Bond formed by the transfer of

electrons from one atom to another

The reaction of sodium and chlorine to produce sodium chloride.

The Ionic Bond

Ionic Bond

• electrostatic attraction

• oppositely charged ions

• metal and a nonmetal

• Electrons transferred

• Extremely strong bonds

COVALENT BOND

The atoms are linked together by

sharing of electrons between the atoms

+

Show bonding in O2

Show bonding in N2

The Covalent Bond

Covalent Bond • sharing of electrons

• nonmetals

• a neutral overall charge

• Electrons not transferred

• Electrons shared

• Weaker bonds than ionic

bonds

Figure 8.2 or another

molecule picture

BOND AND LONE PAIRS

• Valence electrons are distributed

as shared or BOND PAIRS and

unshared or LONE PAIRS.

•

••

•

••

H Cl lone pair (LP)

shared or

bond pair

This is called a LEWIS

structure.

MOLECULAR

GEOMETRY

MOLECULAR GEOMETRY

VSEPR • Valence Shell Electron

Pair Repulsion theory.

• Most important factor in determining geometry is relative repulsion between electron pairs.

Molecule

adopts the

shape that

minimizes the

electron pair

repulsions.

MOLECULAR GEOMETRY

C

H

H

H

H methane, CH4

less repulsion between the

bonding pairs of electrons

109.5° 90°

C

H

H

H

H

NH H

H

C

H

H

H

H

less repulsion between the bonding pairs of electrons

.. ammonia

NH3

.. ..

..

C

H

H

H

H NH H

H

OH H.. ..

..

109.5° (109.5°) 109.5° (107°) 109.5° (104.5°)

water, H2O

C

H

H

H

H NH H

H

OH H.. ..

..

BOND POLARITY

HCl is POLAR because it has a positive end and a negative end. (difference in electronegativity)

Cl has a greater share

in bonding electrons

than does H.

Cl has slight negative charge (-d) and H

has slight positive charge (+ d)

H Cl••

••

+d -d

••

C OO

carbon dioxide

- -

(a nonpolar molecule)

-

-O

H

HWater

a polar molecule

- direction of polarity

Hydrogen bond

In alkanol In amine

– Most of them are liquids in room temperature and pressure.

H – bond formation in Organic compounds

O H OH

N H

HN

HH