How does elements atomic mass differ from its mass number?

•Atomic mass is also known as atomic weight. Atomic mass is the weighted average mass of an atom of an element based on the relative natural abundance of that element's isotopes.

•The mass number is a count of the total number of protons and neutrons in an atom's nucleus.

Explanation:

Atomic Mass Versus Mass Number

1.The mass number is the sum of the number of protons and neutrons in an atom. It is a whole number.

2.The atomic mass is the average number of protons and neutrons for all natural isotopes of an element. It is a decimal number.

3.Atomic mass value sometimes change over time in publications as scientists revise the natural isotope abundance of elements.