Isotopes (Also seen in GCSE Physics 1 and 2)

Isotopes are different forms of an element. They always have the same number of protons but have a different number of neutrons. Since they have the same number of protons (and electrons) they behave in the same way chemically.

Chlorine If we look at Chlorine in the periodic table we see that it is represented by . How can it have 18.5 neutrons? It can’t! There are two stable isotopes of Chlorine, which accounts for ~75% and which accounts for ~25%. So the average of a large amount of Chlorine atoms is .