I II III IV

Chemical Bonding

Chapter 6

Section 1 & 2

Pages 175-189

Chemical Bond Attractive force between atoms or

ions that binds them together as a unit.(valence e- of one atom attracted to the nucleus of another atom).

Bonds tend to form to decrease potential energy or increase

stability. Types are ionic or covalent.

Ionic Bond

A cation is attracted to an anion• Cation = positively

charged ion• Anion = negatively

charged ion

Octet Rule is followed!

Ionic Compounds

Tend to form a crystal lattice.

Highly ordered

Repeating pattern

Ionic Compound metal-nonmetal

Two or more elements are combined in a chemical bond by gaining or losing electrons that achieves the octet rule.

Covalent Bonding nonmetal-nonmetal

A covalent bond is formed by a shared pair of electrons between two atoms.

ElectronegativityUsing Electronegativity values one can determine

the % ionic character.Nonpolar-covalent, equal sharing of electrons.

Bonds having 0% to 5% ionic character. Electronegativity differences of 0 to 0.3.

Polar-covalent, unequal sharing of electrons. Bonds having 5% to 50% ionic character. Electronegativity differences between 0.3 to 1.7.

Ionic bonding, is a complete transfer of electrons. >50% ionic character. Electronegativity differences of 1.7 to 3.3

Molecule; nonmetal-nonmetal

A group of atoms united by covalent bonds. ( polar or non-polar covalent).

Diatomic Molecule

Molecular Substances

Substance made of molecules

DNA

*The law of Octet

Octet Rule:

Atoms tend to gain, lose, or share electrons in order to get a full set of valence electrons.

(usually 8 electrons)

Bond Length

Increases as you go down a group, because the atomic radius increases.

Shorter for multiple bonds.

Multiple Bond LengthTriple bond is shorter than double bond, which is shorter than single bond.

Why? The more electrons in a bond, the stronger the attraction to the positively charged nuclei of the bonding atoms.

Bond Energies KJ/molBond Energies- The amount of energy

required to break a chemical bond and form neutral isolated atoms.

In general the higher the bond energy required the stronger the attraction, the shorter the chemical bond. (Data table on page 182)

Exceptions to the Octet Rule

Exceptions are those that form bonds that either have less than 8e- or more than 8e-

Less than eight:

Hydrogen can form one bond that has 2e-

Boron forms three bonds that contains 6e-

More than eight:

Sulfur can form 6 bonds containing 12e-

Phosphorus can form 5 bonds containing 10e-

Lewis Dot Diagrams

Lewis Structures

The use of dots or other symbols to represent bonded and unshared electrons.

2 shared electronsmake a bond.

Lines show the bond between atoms in a compound.

Structural (lines= 2e- )

How to Draw Lewis Structures:

Step 1 (N) determine the number of electrons Needed for each atom in the compound. Grp’s 14,15,16,17 all need 8. Hydrogen needs 2.

Step 2 (A)determine the number of electrons Available, which is determined by the grp # .

Step 3 N – A = e- Shared (S)

Step 4 A - S = Unshared (U)

Example: Methane CH4

4(2) + 1(8) = 16e-

Step 1 = Electrons Needed N

CCarbon goes in the middle because it is the singular atom.

Step 2 = Electrons Available A

1(4) + 4(1) = 8e-

HH

HH

C

Bonds go between atoms

Each bond uses up 2 electrons

Step 2 = N – A = S

16 – 8 = 8e- Shared

HH

HH

4 Bonds use up 8 electrons (4 x 2 = 8)Unshared ? 8 – 8 = 0

Step 1 determine NStep 2 determine AStep 3 N – A = SStep 4 A – S = U

Step 1: Ammonia NH3

NNitrogen goes in the middle because it is the singular atom.

Arrange Atoms

HH

H

N

Bonds go between atoms (6e-)

Each bond uses up 2 e-

Step 2:Form Bonds

HH

H

N

N = 14 A = 8 S = 6 A – S = 2 Used up 6e- with bonds

2 unshared to complete the

octet You’re done!

complete the octet

HH

H••

Step 1 NStep 2 AStep 3 N – A = SStep 4 A – S = U

Example Formaldehyde CH2O

CYou would have to guess whether C or O goes in the middle?It is Carbon, because it can form the most bonds, and least electronegative!

Arrange Atoms

HH

O

C

Bonds go between atoms

Each bond uses up 2 electrons

Form Bonds

HH

O

C

Had total of 20e- from step 1 Used up 6e- with bonds Need 2 more e- on C Need 6 more e- on O NOT ENOUGH TO GO AROUND

NEED DOUBLE BOND.

Step 3:Distribute remaining electrons

HH

O

Need 2 more e- on carbon to complete octet!

C

Remember the Octet

Rule ! Carbon & Oxygen both

need 8e-. They get 8 by sharing 4

e- between them.

Double Bonds

HH

O••

••••

C Represent double bond

with a double line. You are done!

Double Bonds

HH

O••

••

Double bonds occur in these

molecular compounds;

Oxygen, Carbon Dioxide

Triple Bonds: Nitrogen

Multiple Bonds

Resonance StructuresMolecules that can’t be correctly

represented by a single Lewis diagram.Actual structure is an average of all the

possibilities.Show possible structures separated by a

double-headed arrow.

Example: SO3

OO S O

OO S O

OO S O