A small piece of sodium metal is placed in a flask of chlorine gas. A little water helps expose the sodium so it can react with the chlorine gas. The reaction releases a lot of heat as the ionic ...

Atoms are very small. They have a radius of around 1 × 10 10 metres. This symbol shows that chlorine has 35 particles in the nucleus (protons and neutrons), 17 of which are protons. It also tells ...

An element's atomic number defines it. An element with 17 protons will always be chlorine. However an element's mass numbers can vary, which means that it can have different numbers of neutrons.

The atoms in the reactants are: 1 calcium atom, 2 chlorine atoms, 2 sodium atoms, 2 hydrogen atoms, 2 carbon atoms, and 6 oxygen atoms The atoms in the products are: 1 calcium atom, 2 chlorine atoms, ...

A chemical element is one of those squares on the periodic table that adorns many a classroom wall. Sure. But what is an element really? It is a more subtle question that you might realise.