We also, confusingly, tend to refer to pure substances made of one kind of atom, like chlorine gas, as elements. But these are very different from the isolated atoms depicted on the periodic table.

Chlorine naturally exists as two isotopes, \(_{17}^{35}\textrm{Cl}\) (chlorine-35) and \(_{17}^{37}\textrm{Cl}\) (chlorine-37). The abundance of chlorine-35 is 75% ...