2.2.2 shape of molecule Flashcards
Shape of molecules and ions depend on
Total number of electron pairs around the central atom
2 types of electron pairs
Bonding pairs (e.g. e-s in a covalent bond)
Non-bonding pairs (e.g. lone pairs)
Repel
Electron pairs repel as far as possible
Lone pairs repel more than bonding pairs
Bonding pairs
Pair of electrons involved in bonding
These electrons repel each other equally
Lone pairs
Pairs of electrons that are not involved in bonding
Lone pairs repel each other more than bonding pairs
Each lone pair reduces the bond angle by 2.5
Electron pair repulsion theory
Shape of a molecule is determined by the number of bonding pairs and lone pairs in the outer shell surrounding the central atom
As electrons are negatively charged, each electron pair repels other electron pairs
Electron pairs arrange themselves so that they are as far apart as possible
Lone pairs repel more than bonding pairs
Molecules adopt the shape
That has the lowest energy
Predicting the shapes of molecules
If you know how many pairs of electrons there are in the outer shell of the central atom, you can predict the shape of the molecule
VSEPR
Drawing 3D molecules
Normal line is the bond in the plane of the paper
Dotted wedge is the bond going into the paper away from you
Bold wedge is the bond coming out of the paper towards you
2 electron pairs
Linear, 2 bonding pairs, 0 lone pairs
Straight line
180
3 bonding pairs
Trigonal planar
120
4 electron pairs
Tetrahedral (109.5 each)
3 electron pairs + lone pair
Trigonal pyramid/ pyramidal
107
2 bonding pairs + 2 lone pairs
Bent (v-shape)
104.5
5 electron pairs
Trigonal bipyramidal
120 + 90
