answer:So, at the most basic level, the main difference is the energies of the bonds themselves, especially the vibrational energies. Since isotopes are either slightly larger or smaller than the standard atom, bonds to them vibrate at slightly different energies then they would if it were to a standard atom, and this changes the energy of the bond, and makes a difference in terms of cleavage and formation energies. This can actually be fantastically useful in determining chemical mechanisms, and is known as the ‘kinetic isotope effect’, usually primary and secondary isotope effects. Hydrogen is, naturally, the one that is used most often in these types of experiments, as the isotopes are essentially double and triple the mass of the standard atom, but these effects are still seen for heavier atoms, though you naturally need better and better equipment to tell the difference.