1. Unit 9: Covalent Bonding
Chapters 8 & 9
Chemistry 1K
Cypress Creek High School

2. Lewis Structures Count up total number of valence electrons
Connect all atoms with single bonds
“multiple” atoms usually on outside
“single” atoms usually in center;
C always in center,
H always on outside.
Complete octets on exterior atoms (not H, though)
no unpaired electrons
4) Check
valence electrons match with Step 1
all atoms (except H) have an octet; if not, try multiple bonds
any extra electrons?
Put on central atom

3. Lewis Structure Practice
Carbon tetrachloride
Total valence electrons 32
Central atom
carbon
Bond to each of the chlorines
Fill up the octet of each of the chlorines
Check number of valence electrons
Check octet of each atom Cl Cl C Cl Cl

4. Lewis Structure Practice
Methane (CH4)
Ethyne (C2H2)
Water (H2O) H H C H H C H H O H

5. Diatomic Elements
Some nonmetal elements on the periodic table exist in nature only as pairs called diatomic molecules; bonded covalently
H, O, F, Br, I, N, Cl
Hydrogen Molecule (H2)

6. Molecular Shapes Applies to covalent compounds only.
Use VSEPR steps (valence shell electron pair repulsion):
1) Identify the central atom as the element that can form the most bonds
2) Draw the Lewis dot structure for the molecule
3) Count total # of electron pairs around the central atom
4) Count # of bonding pairs of electrons around the central atom
5) Count # of lone pairs of electrons around the central atom
6) Look at summary chart, identify shape

7. # of e- pairs around central atom
Molecular Shapes
# of e- pairs around central atom
# of bonding pairs of e-
# of lone pairs of e-
Name
Shape 2
linear 3
trigonal planar 4
tetrahedral 1
trigonal pyramidal
angular (bent) 5
trigonal
bipyramidal 6
octahedral

8. Exceptions to Octet Rule
Beryllium
Has 2 valence electrons
Full with 4 valence electrons
Ex: BeI2
Aluminum
3 valence electrons
Full with 6 valence electrons
Ex: AlCl3
Boron
Ex: BH3

9. Expanded Octets
Some atoms bond so they have more than 8e- in the outer level
Occur only around a central nonmetallic atom from period 3 or higher
PCl SF6

10. Molecular Shape Example
What is the shape of water (H2O)?
1) Central atom? oxygen
2) Draw Lewis Dot…
3) # of total electron pairs around central atom? 4
4) # of bonding pairs around central atom? 2
5) # of lone pairs around central atom? 2
6) Refer to chart to identify shape…angular (bent)

11. Molecular Shape Prediction
Try to predict the shape using VSEPR and your shape chart:
1) BCl ) CH ) NH3
Lewis Dot
Central Atom
# e- pairs
# bonded pairs
# lone pairs
Shape