In the case of hydrogen, there are two isotopes: protium and deuterium. Protium is the most common isotope of hydrogen, while deuterium is a heavier isotope. Both protium and deuterium have the same atomic number, which defines the element as hydrogen. However, they differ in their atomic masses due to the presence of an additional neutron in the deuterium isotope.
Protium has one proton and no neutrons, giving it an atomic mass of approximately 1 atomic mass unit (amu). Deuterium, on the other hand, has one proton and one neutron, resulting in an atomic mass of approximately 2 amu.
The relative atomic mass is calculated as the weighted average of the atomic masses of all naturally occurring isotopes of an element, taking into account their relative abundances. Since protium is much more abundant than deuterium, the relative atomic mass of hydrogen is close to 1.
It's important to note that relative atomic masses are relative to the carbon-12 isotope, which is assigned a mass of exactly 12 amu. The relative atomic mass of hydrogen is calculated relative to this standard, considering the abundances of its isotopes. Thus, the relative atomic mass of hydrogen is not zero because it takes into account the different masses and abundances of its isotopes.