It is the mass of an atom in a chemical element. It is roughly equivalent to total neutrons and protons present in the atom. It is expressed in atomic mass units (denoted by u). 1amu is equal to the exactly one-twelfth the mass of 1 atom of C-12 and the relative atomic masses of elements is determined with respect to-12 atom.
Atomic masses of Some Elements
| Elements | Atomic Mass (u) |
| Hydrogen | 1 |
| Carbon | 12 |
| Nitrogen | 14 |
| Oxygen | 16 |
| Sodium | 23 |
| Magnesium | 24 |
| Sulfur | 32 |
| Chlorine | 35.5 |
| Calcium | 40 |
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