Bitesize has changed! We're updating subjects as fast as we can. Visit our new site to find Bitesize guides and clips - and tell us what you think!


Chemical calculations - both Tiers


Isotopes are atoms of an element with the normal number of protons and electrons, but different numbers of neutrons. Isotopes have the same atomic number, but different mass numbers.

The different isotopes of an element have identical chemical properties. However, some isotopes are radioactiveradioactive: A substance that emits radiation is said to be radioactive..

Isotopes of hydrogen

Most hydrogen atoms consist of just one protonproton: A proton is a small particle with a positive charge found in the nucleus of the atom. and one electron [electron: An electron is a very small negatively-charged particle found in an atom in the space surrounding the nucleus. ], but some also have one or two neutronsneutrons: Uncharged sub-atomic particles, with a mass of 1 relative to a proton..

Isotopes of hydrogen

H 1,1111 - 1 = 0
H 2,1112 - 1 = 1
H 3,1113 - 1 = 2

Isotopes of chlorine

Chlorine atoms contain 17 protons and 17 electrons. About 75 per cent of chlorine atoms have 18 neutrons, while about 25 per cent have 20 neutrons.

Isotopes of chlorine

Cl 35, 17171735 - 17 = 18
Cl 37,17171737 - 17 = 20

Back to Chemical calculations index

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.