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
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.
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.
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.