I II III

Lewis Diagrams

Lewis Structures

1) Find your element on the periodic table.

2) Determine the number of valence electrons.

3) This is how many electrons you will draw.

Lewis Structures

Find out which group (column) your element is in.

This will tell you the number of valence electrons your element has.

You will only draw the valence electrons.

• Each column is called a “group”

• Each element in a group has the same number of electrons in their outer orbital, also known as “shells”.

Group 1 = 1 electron

Group 2 = 2 electrons

Group 8 = 8 electrons

Except for He, it has 2 electrons

• The electrons in the outer shell are called “valence electrons”

3, 4, 5, 6, 7

Lewis Structures

1) Write the element symbol.

2) Carbon is in the 4th group, so it has 4 valence electrons.

3) Starting at the right, draw 4 electrons, or dots, counter-clockwise around the element symbol.

C

Lewis Structures

C

1) Check your work.

2) Using your periodic table, check that Carbon is in the 4th group.

3) You should have 4 total electrons, or dots, drawn in for Carbon.

Lewis Structures

C

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Lewis Structures

H

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Lewis Structures

P

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Lewis Structures

Ca

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Lewis Structures

Ar

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Lewis Structures

Cl

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Lewis Structures

Al

On your worksheet, try these elements on your own:

a) H

b) P

c) Ca

d) Ar

e) Cl

f) Al

Octet Rule

Remember…· Most atoms form bonds in order to

have 8 valence electrons.

C. Johannesson

· Hydrogen 2 valence e-

· Groups 1,2,3 get 2,4,6 valence e-

· Expanded octet more than 8

valence e- (e.g. S, P, Xe)

· Radicals odd # of valence e-

Exceptions:

A. Octet Rule

F B FFH O HN O

Very unstable!!

F FF S FF F

Drawing Lewis Diagrams

Find total # of valence e-. Arrange atoms - singular atom is

usually in the middle. Form bonds between atoms (2 e-). Distribute remaining e- to give each

atom an octet (recall exceptions). If there aren’t enough e- to go around,

form double or triple bonds.

Drawing Lewis Diagrams

CF4

1 C × 4e- = 4e-

4 F × 7e- = 28e-

32e- FF C F

F

- 8e-

24e-

B. Drawing Lewis Diagrams BeCl2

1 Be × 2e- = 2e-

2 Cl × 7e- = 14e-

16e-

Cl Be Cl - 4e-

12e-

B. Drawing Lewis Diagrams CO2

1 C × 4e- = 4e-

2 O × 6e- = 12e-

16e-

O C O - 4e-

12e-

Polyatomic Ions

To find total # of valence e-:· Add 1e- for each negative charge.· Subtract 1e- for each positive

charge. Place brackets around the ion and

label the charge.

Polyatomic Ions

ClO4-

1 Cl × 7e- = 7e-

4 O × 6e- = 24e-

31e- OO Cl O

O

+ 1e-

32e-

- 8e-

24e-

NH4+

1 N × 5e- = 5e-

4 H × 1e- = 4e-

9e- HH N H

H

- 1e-

8e-

- 8e-

0e-

Polyatomic Ions

C. Johannesson

Resonance Structures

Molecules 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.

C. Johannesson

Resonance Structures

OO S O

OO S O

OO S O

SO3