Post on 23-Feb-2016
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I II III
Lewis Diagrams
Lewis Structures1) 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 electronGroup 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 Structures1) 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
COn your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) Al
Lewis Structures
HOn your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) Al
Lewis Structures
POn your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) Al
Lewis Structures
Ca
On your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) Al
Lewis Structures
ArOn your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) Al
Lewis Structures
ClOn your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) Al
Lewis Structures
Al
On your worksheet, try these elements on your own:
a) Hb) Pc) Cad) Are) Clf) 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 CF41 C × 4e- = 4e-
4 F × 7e- = 28e-
32e- FF C F
F
- 8e-
24e-
B. Drawing Lewis Diagrams BeCl21 Be × 2e- = 2e-
2 Cl × 7e- = 14e-
16e-
Cl Be Cl - 4e-
12e-
B. Drawing Lewis Diagrams CO21 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