LEWIS DIAGRAMS

Bonding

Types of Chemical Bonds

Lewis Theory for Ionic CompoundsO Atoms and ions are stable if they have a full octet.O Electrons are most stable when they are paired.O Use arrows to represent the transfer of electrons.O The final structure will contain ions.

Ba P

Ba BaP

Example Ba3P2

P23 Ba+2 -3

Lewis Theory for Covalent Compounds

O Atoms are stable if they have a full octet.O Electrons are most stable when they are

paired.O Non-metals will share electrons to obtain

a full valence shell.O A molecules structural formula can be

visualized but constructing a Lewis Structure.

Lewis StructuresO Simple covalent compounds such as CH4

may be done by pairing electrons from different atoms. The pairing is shown with circles.

O More complex covalent compounds and polyatomic ions should be drawn using an alternative method.

Example CH4

C H

H

H

H

C HH

HH

The Process For Drawing Complex LD Diagrams

1. Determine the total number of valence electrons available.

2. Draw the diagram placing the central atom in the middle and the surrounding atoms around it.

3. Put a pair of electrons between the atoms for bonds.

4. Complete the octets for all external atoms.5. If there are electrons left over, place around

the central atom.6. If the central atom does not have a full octet,

use electrons from the external atoms to create a multiple bond between the central atom and an exterior atom.

Example CO3-2

Non-Octet Compounds O Some compounds will contain central

atoms that do not follow the octet rule.

O The four possibilities for non-octet compounds are:

1. Where more than 4 atoms are bonded to the central atom such as PCl5.

2. A noble gas is participating in bonding such as XeF4.

3. Where the central atom has less than 8 valence electrons such as BH3.

4. Where molecules contain an odd number of nonbonding electrons such as NO.N O

Resonance StructuresOFor some molecules, there are multiple ways

of placing the electrons between the atoms.OStructures that differ only in the

arrangement of the electrons are called RESONANCE STRUCTURES.

OResonance structures are indicated using a double headed arrow.

Example CO3-2

CO

OO

2-

CO

OO

2-

CO

O O

2-

Coordinate Covalent BondsOA coordinate covalent bond results when

both electrons in the bond are donated from the same atom.

OTo determine if a bond is coordinate covalent, compare the number of non-bonding electrons around an atom to the number of valence electrons the atom has.

CO

OO

2-O only has 6 valence electrons and since O has3 nonbonding pairs of electrons on it both the electrons in these bonds are coming from C.Coordinate

covalent bonds

HomeworkO Read Section 4.1O Page 200 #1,2O Page 204 #1,2