Question

why postulate 3 and postulate 4 of daltons atomic theory is not applicable after the discovery of isotopes and isobars??

Answer 1

The discovery of isotopes indicated that all the atoms of the same element are not perfectly identical in all respects. Atoms of the same element having different masses are called as isotopes. For example 1H1, 1H2, 1H3. Atoms of different elements are not different in all respects; atoms of different elements having same atomic mass are called as isobar. For example argon and calcium atoms have same atomic mass of 40.