The atomic number of hydrogen is 1, which means it has one proton in its nucleus. However, hydrogen gas (H2) is composed of two hydrogen atoms bonded together. Therefore, the atomic mass of hydrogen gas is the sum of the atomic masses of two hydrogen atoms.
The atomic mass of hydrogen is approximately 1.008 atomic mass units (AMU) per hydrogen atom. So, the atomic mass of hydrogen gas (H2) is calculated as follows:
Atomic mass of hydrogen gas = 1.008 AMU + 1.008 AMU = 2.016 AMU
Therefore, the atomic number of hydrogen is 1, and the atomic mass of hydrogen gas is approximately 2.016 atomic mass units.