Lesley Finn, of Ilam School, asks :-

How many electrons are there in a molecule?

Tim Oughton, a chemist and lecturer in science at the Christchurch College of Education, responded.

Atoms are the basic building blocks of us and all other substances. There are only ninety different types of atoms that occur naturally, ranging from hydrogen, the lightest, to uranium, the heaviest. Their chemistry is determined by the number of electrons they have in orbit around them, ranging from one for hydrogen to 92 for uranium.

Atoms are very small, so small that, for example, the number of aluminium atoms contained in a square centimeter of aluminium foil is over a million million times the population of the world.

All molecules are chemical combinations of atoms which usually swap or share some of their electrons in order to form stable combinations. For example, a molecule of hydrogen gas consists of two hydrogen atoms, a water molecule is a combination of two hydrogen and one oxygen atoms, petrol is made up of carbon and hydrogen atoms and sugar is made up of carbon, hydrogen and oxygen atoms.

We currently know that more than 5 million different types of molecules exist and more are being discovered all the time, in nature or by being made in chemical laboratories. So it is not possible to talk about the average number of electrons in a molecule. They range from the hydrogen molecule, the lightest molecule, which contains only two electrons, through to the extremely complex molecules on which life depends, such as the D.N.A. molecules, which contain over a million electrons.