Isotopes:

In the individual atoms of a given element, like oxygen, the number of neutrons can differ. Despite of the number of neutrons, though, the element remains its identity based on the atomic number. Differing numbers of neutrons outcome in various isotopes for a particular material element.

Each element has one specific isotope which is found most frequently in nature. Though, all elements have more than one isotope, and some have many. Varying the number of neutrons in an element's nucleus outcomes in a dissimilarity of mass, and also a difference in density, of the element. Therefore, for illustration, hydrogen having a neutron or two in the nucleus, all along with the proton, is known as heavy hydrogen. In general, the occurring form of uranium has three more neutrons in its nucleus than the type that is notorious for use in atomic weapons.

Adding or taking away neutrons from the nucleus of an element is not quite as unbelievable a business as adding or taking away protons, though it is still a task usually transferred to high-energy physics. You cannot simply take a balloon filled with air, that is around 78 % nitrogen, and make it more massive by injecting neutrons into the nitrogen nuclei.