 An element is a chemical substance made up of a particular kind of atom and hence cannot be broken down or transformed by a chemical reaction into a different element, though it can be transmuted into another element through a nuclear reaction.This is so because all of the atoms in a sample of an element have the same number of protons, though they may be different isotopes, with differing numbers of neutrons.As of 2019, there are 118 known elements, about 80 of which are stable – that is, they do not change by radioactive decay into other elements.