All atoms are made up of three subatomic particles, the proton, neutron and electron

The proton has a +1 charge. It is a fairly heavy particle and resides in the dense nucleus of an atom

The electron has a -1 charge. It is a light particle with a mass ~1/2000 of a proton. It resides in a cloud around the nucleus

The neutron has a 0 charge. It is a heavy particle with a mass about equal to a proton and resides in the nucleus

The number of protons, neutrons and electrons in an atom determines the element, isotope and ionic state in that order.

Information provided by: http://learn.chem.vt.edu