Atoms of same kind of matter can have different size and mass.
So is it possible that they will also have different chemical properties or the chemical properties always stay identical for every atom??

Dear student

There are three kinds of matter, solid, liquid and gas
Let us take an example of different types of gases : Oxygen O₂ and hydrogen H₂
Now, oxygen gas has same kind of atoms i.e. oxygen atoms hence chemical property of every atom of oxygen is same.
Atomic mass of 1 oxygen atom is 16, atomic number is 8; so every oxygen atom would have 8 electrons and sum of protons and neutrons would be 16.
so, chemical property of every oxygen atom is different.
hydrogen gas has same kind of atoms i.e. hydrogen atoms hence chemical property of every atom of hydrogen is same.
Its atomic mass and atomic number is 1 which means every atom of hydrogen contain 1 electron and 1 proton.

so, chemical property of every hydrogen atom is similar

Regards