Covalent bonding and VSEPR
Steps for determining molecular geometry
1) Draw the Lewis Structure for the molecule (review the correct steps for drawing Lewis Structures if needed)
2) Count the number of “things” that surround the central atom
a. “THINGS” include
i. Bonds (doesn’t matter if it is a single, double, or triple bond…just count the total bonding
domains)
ii. Electron pairs
3) Determine what structure the molecule is based on
a. If there are just TWO total “things”, it is based on the “LINEAR” electron domain geometry
b. If there are THREE total “things”, it is based on the “TRIGONAL PLANAR” electron domain geometry
c. If there are FOUR total “things”, it is based on the “TETRAHEDRAL” electron domain geometry
d. If there are FIVE total “things”, it is based on the “TRIGONAL BIPYRAMIDAL” electron domain
geometry
e. If there are SIX total “things”, it is based on the “OCTAHEDRAL” electron domain geometry
4) Which atoms are replaced by lone electron pairs?
5) What is the final structure, and what are the bond angles?
a. Final structure possibilities from the possible structures listed in step 3: (bonds/unshared pairs of
electrons)
i. TWO things:
1. Just linear (2/0)
ii. THREE things:
1. Trigonal Planar (3/0)
2. Bent (2/1)
iii. FOUR things:
1. Tetrahedral (4/0)
2. Trigonal Pyramidal (3/1)
3. Bent (2/2)
iv. FIVE things:
1. Trigonal Bipyramidal (5/0)
2. Seesaw (4/1)
3. T-Shaped (3/2)
4. Linear (2/3)
v. SIX things:
1. Octahedral (6/0)
2. Square Pyramidal (5/1)
3. Square planar (4/2)
b. Bond angles:
i. Linear = 180 degrees
ii. Trigonal Planar = 120 degrees
iii. Trigonal pyramidal = a little less than 120 degrees…usually about 105 degrees
iv. Tetrahedral = 109.5 degrees
v. Trigonal bipyramidal = think of it as a LINEAR combined with a TRIGONAL PLANAR
vi. Octahedron = 90 degrees
Do Molecular Geometry Practice Problems On The Pages That Follow!
CO2
BF3
CH4
H2O
AsF3
BeH2
SeO2
SCl2
SeF6
IF3
ICl4-
SO2
NO3-
HCN
CI4
PCl5
CO32-
BH4-
BrF5
KrF4
SF6
TeF4
TeH2
ClF3
XeF2
KrF4
CH2Cl2
BrO4-