NCHE 221-Lewis Structures
NCHE 221-Lewis Structures
NCHE 221-Lewis Structures
1A
2A 3A 4A 5A 6A 7A
The bond arises from the mutual attraction When one nonmetal shares one
of 2 nuclei for the same electrons. or more electrons with an atom
of another nonmetal so both
HA + HB HA HB atoms end up with eight
valence electrons
A covalent bond is a balance
of attractive and repulsive forces.
SHARING OF ELECTRONS IN COVALENT BONDS
F + F F F
Lewis structure of F2
H + O + H H O H or H O H
2e-8e-2e-
O C O or O C O
8e- 8e- 8e- double bonds
double bonds
Triple bond – two atoms share three pairs of electrons
N N or N N
8e-8e-
triple bond
triple bond 6
Polar Covalent Bond
A covalent bond with greater electron density around
one of the two atoms
electron rich
electron poor
region
region e- poor e- rich
H F H F
d+ d-
Classification of Bonds
Difference in EN Bond Type
0 Covalent
2 Ionic
0 < and <2 Polar Covalent
F N F
F
Write the Lewis structure of the carbonate ion (CO32-).
Step 1 – C is less electronegative than O, put C in center
Step 2 – Count valence electrons C - 4 (2s22p2) and O - 6 (2s22p4)
-2 charge: + 2e-
4 + (3 x 6) + 2 = 24 valence electrons
Step 3 – Draw single bonds between C and O atoms
2-
O C O
O
Resonance
2- 2- 2-
- - - -
O C O O C O O C O
O O O
- -
Exceptions to the Octet Rule
Be – 2e-
BeH2 2H – 2x1e- H Be H
4e-
Odd-Electron Molecules
N – 5e-
NO O – 6e- N O
11e-
The Expanded Octet (central atom with principal quantum number n > 2)
F
F F
S – 6e- 6 single bonds (6x2) = 12
SF6 6F – 42e- S 18 lone pairs (18x2) = 36
48e- Total = 48
F F
F
Shapes of molecules
Problems and questions —
• How is a molecule or polyatomic ion held
together?
• Why are atoms distributed at strange
angles?
• Why are molecules not flat?
• Can we predict the structure?
• How is structure related to chemical and
physical properties?
1. Linear (straight line)
Ball and stick
model