Difference between Isotopes and Isobars Isotopes Isobars 1. They have the same atomic number but different mass numbers. 2. They have identical electronic configuration. 3. They occupy the same place in the periodic table. 4. Their chemical properties are identical. 5. They have the same number of protons and electrons but different number of neutrons. 1. They have the same mass number but different atomic numbers. 2. They have different electronic configurations. 3. They occupy different places in the periodic table. 4. Their chemical properties are different. 5. They have unequal number of protons, electrons and neutrons.