Atomic structure

Atoms

The structure of the atom

All substances are made from atoms [atoms: An atom is the smallest part of an element that still has the properties of that element, comprising electrons surrounding a nucleus of protons and neutrons. ]. Atoms have a small central nucleus [nucleus: The central part of an atom. It contains protons and neutrons, and has most of the mass of the atom. ] surrounded by even smaller particles called electrons [electrons: Sub-atomic particles, with a negative charge and a negligible mass relative to protons and neutrons. ].

The nucleus is positively charged, and the electrons are negatively charged.

Elements

Any given element [element: A substance made of one type of atom only. ] is made of atoms of just one particular sort. The atoms of any element are different to the atoms of any other element. So iron is made from a different sort of atom to sulfur, and carbon atoms are different to oxygen atoms.

Chemical symbols

The atoms of each element are represented by chemical symbols. These usually consist of one or two different letters. Three letters are sometimes used for newly discovered elements.

The first letter in a chemical symbol is always an UPPER CASE letter. The other letters are always lower case. So the symbol for magnesium is Mg, and not mg, MG or mG.

Every element has its own chemical symbol. For example, iron is Fe, sulfur is S, sodium is Na, and oxygen is O.