14.1 Shapes of Molecules and Ions
Remember that a negative charge centers refers to the number of pairs electrons around the central atom. This includes both the lone (non
bonding pairs) pairs and bonded pairs of electrons in single, double or triple bonds. Each double and triple bond counts as one negative charge
center. The shape according to VSEPR theory results in five basic shapes for 5 and 6 negative charge centered molecules and ions. The overall
shape depends on the number of bonding and lone pairs of electrons around the central atom. The overall bond angle is the angle between the
bonded atoms attached to the central atom. To determine the overall shape and bond angle using VSEPR theory the number of bonding and lone
pairs of electrons around the central atom needs to first be determined.
Number of
negative
charge
centers
Number
bonding
pairs of
electrons
Number of
lone / nonbonding pairs
of electrons
Overall Shape
(according to VSEPR)
Bond Angle between
attached atoms
(according to VSEPR)
Examples
6
6
0
Octahedral
90°
SF6
5
5
0
Trigonal bipyramid
90° & 120°
PF5
6
4
2
Square planar
90°
XeF4
1
2D Structural formula drawn
in shape with angles between
attached atoms
5
3
2
T-shape
∼180° & ∼90°
ICl3
6
5
1
Square pyramid
~88°
BrF5
5
4
1
Saw horse
90° & ∼120°
SF4
5
2
3
Linear
180°
XeF2
As with other molecules and ion, according to VSEPR theory the lone pairs and bonding pairs of electrons are arranged around the central atom so
as to minimize the repulsion between the lone and bonding pairs of electrons. The relative magnitude of the electron pair repulsions is:
Lone pair - lone pair > bonded pair - lone pair > bonded pair - bonded pair repulsion
2
Formula
Lewis dot and cross
diagram
Structural formula
(drawn in the correct
shape)
Number
negative
charge
centers
# Bonding
pairs earound
central atom
BrF3
PF5
SCl4
SF6
XeF4
BrF5
PCl6-
SF4
3
# lone pairs
of e- around
central
atom
Bond Angle
(according
to VSPR)
Overall
Shape
(according
to VSPR)
Polar or non
polar
covalent
ANSWERS
Formula
Lewis dot and cross
diagram
Structural formula
drawn in the correct
shape
Number
negative
charge
centers
Number of
bonding
pairs of
electrons
around
central
atom
Number of
lone pairs of
electrons
around
central
atom
Bond Angle
(according
to VSPR)
Overall
Shape
(according
to VSPR)
Polar or non
polar
Polar or non
polar
BrF3
Non Polar,
Symmetrical
PF5
SCl4
SF6
XeF4
BrF5
4
PCl6-
SF4
5