Question

are all the atoms on earth of same size?

Answer 1

All atoms are not of the same size. Different elements that are known to us today have different number of protons, electrons and neutrons. Every element has a characteristic atomic number which defines the properties of the elements. The electrons in an atom are arranged around the nucleus in different energy shells. As the number of electrons for each element is different, they will have different arrangement of electrons in shells around the nucleus and hence size of atoms belonging to different elements is different.

Only the atoms of the same element will have the same size.