Question

What is the atomic mass in hydrogen?

Answer 1

Atomic mass of any element is the number of protons and neutrons in that atom. Atomic mass is measured and expressed in atomic mass units, amu. While, the expression of this mass in grams is called gram atomic mass. Gram atomic mass of an atom is equal to Avogadro number, $6.022\times {{10}^{23}}$ of atoms. 1 amu = $1.66\times {{10}^{-24}}g$.

Complete answer:
Hydrogen is the first and the lightest element of the periodic table, which contains only 1 electron, and so has an atomic number of 1. Apart from 1 electron, an isolated hydrogen atom contains 1 proton, and no neutrons.
The atomic mass of any element is the sum of the mass of protons and neutrons. As the mass of 1 proton is, $1.67\times {{10}^{-24}}g$ or 1.007 u, therefore this is the mass contained in a hydrogen atom. However, this mass resembles the atomic mass unit which is $1.66\times {{10}^{-24}}g$. As this factor is simplified as 1.007 amu, therefore, hydrogen has a mass of 1.007 amu.
Hence, the atomic mass of hydrogen is 1.007 amu, which is $1.66\times {{10}^{-24}}g$

Note:
Hydrogen has 3 isotopes, protium, deuterium and tritium. Protium consist of 1 electron and 1 proton, without any neutron, hence it has 1.007 amu as its atomic mass, while deuterium, has 1 electron, 1 proton, and 1 neutron, so it has a mass of 2.014 amu, while tritium has 1 electron, 1 proton, and 2 neutrons, so it has an atomic mass 3.021 amu. For isotopes, average atomic mass is considered.