Question

Atomic mass of an element is sometimes double the atomic no. But someothers are decimals. Is there a reason for this ? How are atomic masses found ?

Answer 1

The exact atomic masses can be decimals because, the mass of
Proton = 1.007 amu
Neutron = 1.008 amu
Upon adding these when exact masses are considered the addition comes in decimals.

Atomic masses are found by various experiments using sophisticated instruments.