Top 20 facts about atoms
Atoms are tiny particles which build together to make every substance. An atom is the tiniest bit of any pure substance or chemical element. You could fit two billion atoms on the full stop after this sentence. The number of atoms in the Universe is about 10 followed by 80 zeros. Atoms are mostly empty space dotted with a few even tinier particles called subatomic particles. In the centre of each atom is a dense core, or nucleus, made from two kinds of particle: protons and neutrons. Protons have a positive electrical charge, and neutrons none. Both protons and neutrons are made from different combinations of quarks (see quarks). If an atom were the size of a sports arena, its nucleus would be just the size of a pea. Around the nucleus whizz even tinier, negatively-charged particles called electrons (see electrons). Atoms can be split but they are usually held together by three forces: the electrical attraction between positive protons and negative electrons, and the strong and