AS - Bonding

Key learning for this topic

To begin with, go back and check that you fully understand what covalent, ionic and metallic bonding is. Use this to explain the physical properties of ionic, metallic, giant covalent and monatomic substances as well as simple molecules. It is not worth starting the A-Level part until you have completely refreshed yourselves with this first.

The only bond that you may not have met at GCSE is the dative covalent or coordinate bond. This is simply a bond in which both bonding electrons have been provided by one atom, rather than sharing. This is particularly common when a proton joins a lone pair, such as in NH4+ ions but is also in AlCl4- which we will see in Benzene reactions later on. The bond is drawn as a normal "stick", however, there is an arrow head pointing from the atom that provides the electrons towards the other, N → H

Shapes: I always struggle with where to start on this topic but I am happy with this year's attempt. You need to understand that electron pairs repel. This is bonding pairs and lone pairs. Valence Shell Electron Pair Repulsion theory (VSEPR) explains the shapes of molecules. I am not going to bother trying to draw them when I could not compete with this masterpiece: Compound Interests' Shapes infographic. And yes, you have to learn them and their bond angles.

Next we have electronegativity. You need to learn the definition:

Electronegativity is the ability of an atom to attract the pair of electrons in a covalent bond.

If one atom is more electronegative than another (by more than 0.5 on Pauling's scale), then the molecule is polar (as long as there is a dipole moment. You must ensure that the polar bonds do not cancel each other out.

Finally, the boiling points, melting points (and even fluidity) of molecules can be explained and predicted by inter-molecular forces and their relative strengths.

This page was updated on: 1st November 2023