Isotopes: Isotopes are atoms of the same element having the same atomic number but different atomic masses. Note that the difference in the masses of isotopes is due to the different number of neutrons in their nuclei. Isotopes have the same chemical properties . because they have the same number of electrons. Isotopes have different physical properties because they have different number of neutrons.
Isobars: Nuclei of atoms of different elements which have the same mass number but different atomic number are called isobars. For example 20Ca40 and 18Ar40 are isobars. They have entirely different chemical and physical properties.
