What is the reason for the slightly different physical properties of all the isotopes of an element?

What is the reason for the different atomic masses of the isotopes of an element?

What is the reason for the identical chemical properties of all the isotopes of an element? Explain with the help of an example.

Explain why, the atomic masses of many elements are in fractions and not whole numbers.

Which of the following are isotopes and which are isobars?

Argon, Deuterium, Calcium, Tritium, Protium