An atom is made up of three different parts: protons, neutrons and electrons.

Protons are located in the nucleus, have a mass of 1 a.m.u (atomic mass unit) and have a positive charge (+1)

Neutrons are located in the nucleus, have a mass of 1a.m.u and have no charge (0)

Electrons are located orbiting the nucleus, have a mass of 1/1840 a.m.u and have a negative charge (-1)

The atomic number of an element is the number of protons located in the nucleus of that element.

The mass number is the sum of the number of protons and neutrons in the nucleus.

The electrons are arranged with a maximum of two in the first shell and a maximum of eight in all other shells.

This is called the electronic configuration.

Atoms always have no charge because the number of protons and electrons is the same.

An ion is a charged particle. In an ion the number of protons and electrons is different

	Created by Shane Buckley over 8 years ago

Set of definitions and explanations relating to the atom for Junior Certificate level Chemistry.