Shapes of Molecules and VSEPR Theory

Electron Pair repulsion theory

the shape of a molecule or ion is governed by the arrangement of the electron pairs around the central atom

VSEPR Theory

groups of electrons around the atom will repel each other and therefor take up positions in space as far apart as possible

group of electrons are;

• shared pair forming a bond

• 4 electrons forming a double bond

• 6 electrons forming a triple bond

• unshared pair of electrons - lone pair

order of repulsion

lone pair lone pair > bonding pair - lone pair > bonding pair - bonding pair

lone pairs decrease the b.p - b.p angle by

2-2.5 degrees

2 electron groups (2.bp)

shape name, bond angle, examples

linear

180*

BeCl₂

3 electron groups - 3 b.p

shape name, bond angle, examples

trigonal planar

120

BF3 BCl3

3 electron groups - 2 b.p + 1 l.p

shape name, bond angle, examples

bent/ v shape

120

SO2

4 electron groups - 4 b.p

shape name, bond angle, examples

tetrahedral

CH4

109.5

4 electron groups - 3 b.p + 1 l.p

shape name, bond angle, examples

trigonal pyramidal

107

NH3 and H3O+

4 electron groups - 2.bp -2.bp

shape name, bond angle, examples

bent

105

h20

5 electron groups - 5 b.p

shape name, bond angle, examples

trigonal bipyramidal

90 and 120

PCl5

5 electron groups - 4 b.p - 1.l.p

shape name, bond angle, examples

seesaw or sawhorse

90 120

SF4 and XeO2F2

5 electron groups - 3 b.p + 2 l.p

shape name, bond angle, examples

t- shaped

90

ClF3

5 electron pairs; 2 b.p + 3 l.p

shape name, bond angle, examples

linear

180

I₃^-

6 electron pairs - 6 b.p

shape name, bond angle, examples

octahedral

90

SF6

6 electron pairs - 5 b.p + 1 l.p

shape name, bond angle, examples

square pyramidal

90

XeOF4

6 electron pairs - 4 b.p + 2 l.p

shape name, bond angle, examples

square planar

90

ClF₄^- and XeF₄

6 electron pairs- 3.bp + 3 l.p

shape name, bond angle, examples

T- shaped

90

6 electron groups 2 B.P + 4l.p

shape name, bond angle, examples

linear

180