Shapes of molecules and ions Flashcards
For each question you must do: 1) A sketch of the shape 2) The name of the shape 3) The bond angle 4) Explanation of the shape
What is the order of strength of repulsion?
Lone pair ↔︎ Lone pair
Lone pair ↔︎ Bonding pair
Bonding pair ↔︎ Bonding pair
An molecule will take up a shape to minimise repulsions.
2 bonding pairs
BeCl2
Sketch the shape
Linear
Bond angle = 180º
2 bonding pairs of electrons repel each other equally and the molecule takes up this shape to minimise repulsions.
3 bonding pairs
BF3
Sketch
Trigonal planar
Bond angle = 120º
3 bonding pairs of electrons repel each other equally and the molecule takes up this shape to minimise repulsions
4 bonding pairs
CH4, NH4+
Sketch
Tetrahedral
Bond angle = 109.5º
4 bonding pairs of electrons repel each other equally and the molecule takes up this shape to minimise repulsions.
2 sets of bonding pairs
CO2
Sketch
Linear
Bond angle = 180º
2 sets of bonding pairs of electrons repel each other equally and the molecule takes up this shape to minimise repulsions
5 bonding pairs
PF5
Sketch
Trigonal bipyramidal
Bond angle = 90º and 120º
5 bonding pairs of electrons repel each other equally and the molecule takes up this shape to minimise repulsions.
6 bonding pairs
SF6
Sketch
Octahedral
Bond angle = 90º
6 bonding pairs of electrons repel equally and the molecule takes up this shape to minimise repulsions.
3 bonding pairs, 1 lone pair
NH3, H3O+
Sketch
Pyramidal
Bond angle = 107º
3BP, 1LP of electrons, the LP has a greater repulsions than the bonding pairs and the molecule takes up this shape to minimise repulsions
2 bonding pairs, 2 lone pairs
H2O, BrF2+
Sketch
Bent
Bond angle = 104.5º
2BP, 2LP of electrons, the lone pairs of electrons have a greater repulsion than the bonding pairs of electrons and the molecule takes up this shape to minimise repulsions.
3 bonding pairs, 2 lone pairs
BrF3
Sketch
T shaped
Bond angle = 86º
3BP, 2LP of electrons, the lone pairs of electrons have greater repulsion than the bonding pairs of electrons and the molecule takes up this shape to minimise repulsions.
4 bonding pairs, 2 lone pairs
BrF4-
Sketch
Square planar
Bond angle = 90º
4BP, 2LP of electrons, the lone pairs of electrons have a greater repulsions than the bonding pairs of electrons and the molecule takes up this shape to minimise repulsion.
2 bonding pairs, 3 lone pairs
XeF2
Sketch
Linear
Bond angle = 180º
2BP, 3LP of electrons, the lone pairs of electrons have a greater repulsion than the bonding pairs of electrons and the molecule takes up this shape to minimise repulsion.
What can atoms such as Xe and Br do?
They can promote an electron to a higher energy subshell in in order to facilitate the bonding.
e.g. in BrF3, one electron is promoted to a higher subshell in order to have 3 unpaired electrons and 2 lone pairs.
In XeF2, Xe promotes one electron in order for it to have two unpaired electrons and 3 lone pairs of electrons.
