# How can elements have different isotopes?

May 12, 2018

Because elements CAN have different numbers of nuclear particles....

#### Explanation:

The nucleus of every atom is composed of massive particles: $\text{protons}$, with a positive electrostatic charge; and $\text{neutrons}$, the which are neutrally charged. The NUMBER of protons DEFINES the atomic number absolutely...and ${Z}_{\text{the atomic number}}$ DEFINES the identity of the element:

$\text{Z = 1, hydrogen; Z = 2, helium; ..... Z = 92 uranium}$

The number of neutrons, defines the identity of the isotope.. For protium, ""^1H, there is one nuclear particle, the defining proton. For deuterium, ""^2H, there are TWO nuclear particles, the defining proton, and a neutron. For tritium, ""^3H, there are THREE nuclear particles, the defining proton, and TWO neutrons.

As $Z$ increases, isotopic substitution becomes more common, and the atomic mass quoted on the Periodic Table is the weighted average of the individual isotopes.