If you need a refresher from GCSE, start with this quick introduction to bonding from TedEd. You might also like to clear up any misconceptions you have about ionic and covalent bonds using this true/false quiz (scroll past the answers on the first two pages to page 3 – no cheating!) before delving deeper.
And when you think you’ve got a handle on it all, there’s an excellent article on whether chemical bonds are real or figments of our imagination on the Chemistry World website 😍.
Ionic bonding and ionic lattices
Ionic bonding is the electrostatic attraction between oppositely charged ions – it is not the transfer of electrons from one atom to another to form the ions themselves.
Cations are positively charged and anions are negatively charged.
How to write an ionic equation
An ionic equation describes the actual chemical reaction that occurs when we add drops of aqueous sodium chloride to a solution of silver nitrate, or when we place a piece of magnesium ribbon in a solution of zinc sulfate.
Metallic bonding and properties of metals
The free electron model of metallic bonding describes a metallic lattice of cations surrounded by a sea of delocalised valence electrons (this is the model you will be familiar with from GCSE).
Covalent bonding
Covalent bond is a shared pair of electrons between two non-metal atoms (predominantly), and there is a strong electrostatic attraction between the nuclei of each atom and the shared pair.
A note on the nature of ionic lattices
We are all familiar with the classic picture of an ionic lattice – for example, for a compound such as sodium chloride where sodium and chlorine exist as discrete ions in a regular 3-D arrangement.
Let’s take a look at the evidence for the model and its limitations …
Using valence bond theory to explain sigma and pi bonds
Our familiar model of covalent bonding is largely based on the Lewis model, with atoms sharing pairs of bonding electrons and everyone obeying the octet rule.
It is often very successful in explaining the structures of molecules, and the bonding that gives rise to those structures, but there are many exceptions.
Valence bond theory is particularly useful for describing bonding in organic carbon-based molecules.
Molecular orbital theory
In molecular orbital theory covalent bonds are the result of atoms combining atomic orbitals to form new molecular orbitals.
Giant covalent (macromolecular) networks and simple molecules
You need to be able to explain the properties of giant covalent networks / lattices in terms of their structure and their bonding – they are not the same things.
Structure is about the arrangement of atoms, bond angles, how many bonds are being made. Bonding is covalent vs. intermolecular.
Shapes of molecules and polyatomic ions
Working out the shape of a molecule or a bond angle always starts with a dot and cross diagram.
If we know how many pairs of electrons (bonding pairs or lone pairs) surround the central atom in the molecule, then working out the shape is simple.
Electronegativity and polar bonds
Electronegativity is the power of an atom in a molecule to attract electrons toward itself – we are typically talking about two atoms that are covalently bonded, with the more electronegative of the atoms pulling the shared pair of bonding electrons away from the less electronegative atom.
What is intermolecular bonding?
All intermolecular bonds arise from the attraction between dipoles in molecules. There are three types of intermolecular bond:
- hydrogen bonds
- permanent dipole – permanent dipole intermolecular bonds
- instantaneous dipole – induced dipole intermolecular bonds which are also known as London forces