Question

Why is the atomic weight is also called as the relative atomic mass. Explain in a way I can understand.

Answer 1

Atomic mass has the unit amu . This is a relative unit. Let us consider an example. We have 3 bodies A, B, C each having mass 10kg 20kg and 40kg. If we consider the mass of A i.e. 10kg to be the relative unit, then the mass of B is 2 relative unit and C is 4 relative unit. Its the same case with atoms. But in case of 10kg defined as 1 relative unit in our example we have 1 amu defined as the mass of 1/12 of carbon 12 isotope. Hence atomic mass of every element is expressed in terms of multiple of mass 1/12 of carbon 12 isotope and so it is called relative atomic mass.
But actually relative atomic mass and atomic mass are a little different. Its clear by the following example:
Atomic mass of oxygen = 16amu
Relative atomic mass of oxygen = 16

Hope you understand.