Why ICE floats on
Why ICE floats
WATER ? ?
on WATER ? ?
Why doesn’t ICE
behave as most
solid & sink ?
volume of ICE
>
volume of water ?
How would the
shapes/structure of
ICE affect its density
?
Valence Shell Electron Pairs
Repulsion [VSEPR]
Electron pairs tend to
arrange themselves in such
a way to minimise
repulsion.
Valence Shell Electron Pairs Repulsion [VSEPR]
Two types of electron pairs
 Lone pairs
 Bond pairs
Valence Shell Electron Pairs Repulsion
[VSEPR]
Lone pairs electrons (not
involved in covalent bonding)
are closer to the nucleus
Lone pair electrons would
have a greater repulsion force
compare with bond pair
electrons.
Lone-pair - lone-pair
repulsion >
lone pair-bond pair
repulsion >
bond pair-bond pair
repulsion
1 Draw the Lewis structure of molecules
2 (a) Count the no. of bond pair electrons
(b) Count the no. of lone pair electrons
3 (a)Apply the VSEPR theory
(b)Determine the shape of molecules
BeCl2
linear
http://www.chemguide.co.uk
H2 O
V-shape/bent
http://www.chemguide.co.uk
BF3
Trigonal
planar
http://www.chemguide.co.uk
NH3
Trigonal
pyramidal
http://www.chemguide.co.uk
Predict the shapes of
1. CO2
2. H2S
3. AlCl3
4. NCl3