The word nuclides is used to describe any atomic species of which the proton number and the nucleon number are specified. nuclides are written as symbol.
When an element has relative atomic mass which is not a whole number,it is because it consist of a mixture of isotopes. istopes are nuclides of the same element. They have the same atomic number but different mass number i.e they differ in the number of neutrons in the nucleus. since chemical properties depend upon the nuclear charge and electronic structure of an atom,with mass having little effect,isotopes show the same chemical behaviour.the isotopes of chlorine,have the same atomic number,17.the different between the mass number shows that one isotope has 18 neutrons and the other has 20 neutrons. the chemical reactions of the twob isotopes are identical. their names can be written as chlorine-35 and chlorine-37.