Shapes of Molecules and Ions

Question 1

What is the shape of a molecule determined by?

Answer 1

Determined by the number of electrons pairs in the outer (valence) shell of the central atom
– Electron pairs repel each other to try to get as far apart as possible

Question 2

What is the order of repulsion between electron pairs?

Answer 2

Lone Pair - Lone Pair (strongest)
Lone Pair - Bonding Pair
Bonding Pair - Bonding Pair (weakest)

Question 3

How can you predict the shape of a molecule/ ion without double bonds?

Answer 3

1) Count the number of outer electrons on the central atom
2) Add 1 for every atom bonded to the central atom
3) For ions add one for singly negative/ minus one for singly positive.
4) Total and divide by 2 to get number of electron pairs
5) Deduce the regular shape taken by this number of pairs
6) Alter for any long pairs needed.