all atoms have different masses Mass of an atom is due to protons and neutrons present in an atom and number of proton is something that distinguish between atoms, therefore mass of hydrogen is...
16 nucleons versus 1 , so about 16 times as dense, higher boiling point
8 protons versus 1, so 8 electrons versus 1, which means :-
2 electrons in the outer shell versus 1, different valency and...