How To Write Chemical Formulas

How To Write Chemical Formulas

This VideoJug video teaches how to write different kinds of chemical formulae. The key is to take note of the valency of each element and swap it in combining the two elements, therefore producing an electrically neutral molecule. This also includes molecules composed of two or more elements.

Hi! I am Donald Sinclair. I am a science teacher with Greater London Tutors, and today, we are going to be looking into a few topics in Chemistry. This is how to write chemical formulae.

When writing chemical formulae, the key thing to remember is the valency of the components of the molecule, for example, Aluminium Oxide. Aluminium, which we can see from the Periodic Table, has a valency of 3, as it is in group 3. This means that an Aluminium ion has a charge of positive 3.

Oxygen, is in group 6, which means that it has a valency of 2. So, an oxide ion has a charge of minus 2. This means if we make a molecule which is electrically neutral, you're going to have to have 3 oxygens to give a charge of minus 6, combining with 2 Aluminiums for a charge of positive 6.

So when we write Aluminium Oxide, simply swap these numbers around to give Al2O3 or Aluminium Oxide, or possibly you can cancel. For example, Aluminium Phosphide, Aluminium, as we've just seen, has a valency of 3. Phosphorus, which is in group 5, has a valency of 3 as well.

This means that you can write Aluminium Phosphide as Al3P3, but these threes can be cancelled to give a simpler AlP for Aluminium Phosphide. Some molecules contain groups which are not elements. The foremost column as seen once are Hydroxide and Nitrate, which have a valency of 1 and Carbonate and Sulfate, which have valencies of 2.

So for example, Calcium Carbonate; Calcium has a valency of 2 being group 2 and Carbonate has a valency of 2 as well, which means Calcium Carbonate is written as CaCO3. For something like Aluminium Sulfate, Aluminium has a valency of 3 and Sulfate has a valency of 2. This means it's written Al2 and the Sulfate is written with a 3 after it.

However to show it's all one group, it's written in brackets, so we end up with Al2(SO4)3, which is Aluminium Sulfate. .