The mass of a H-atom is less than the sum of the masses of a proton and electron. Why is this?

Explanation

Einstein.s energy - mass equivalence gives
`E=mc^2`
where E=energy
m=equivalent mass of energy
c=speed of light
`m=E//c^2`
If B is the binding energy of hydrogen atom (=13.6eV), then the equivalent mass of energy is given by
`m=B//c^2`
`therefore` Mass of H-atom =`m_p+m_e-B/c^2`
where `m_p` is the mass of a proton and `m_e` is the mass of electron
Thus, `m_p+m_e-B/c^2 lt m_p+m_e`