# Atomic Mass

Atomic Mass:

The mass of a atom of an element is called the atomic mass of that element.

Atoms are infinitesimally small. Both the actual size and the mass of an atom are actually so small that they are beyond our common sense of conception.

This is obvious when we realise that there are $6.023 \times 10^{23}$ atoms in 1 gram of hydrogen or in other word the mass of a hydrogen atom , which is the lightest atom of all atoms , is $1.67 \times 10^{-24}$ gram.

Uranium atom is 238.5 times heavier than that of hydrogen atom and the masses of other neutrally occurring common atoms falls under these mass limits. It was felt very inconvenient to write the mass of an atom or element in gram and a smaller unit of mass was needed to make the measurement of atomic mass easier.

Chemist choose an atom of hydrogen as a standard of mass for denoting masses of different atoms. Up to the year 1908 , hydrogen was the arbitrary standard of comparison and the atomic mass was defined as the average relative mass of atom of an element compared with the mass of a hydrogen atom taken as one.

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