princess Anu:
If by any chance you don't get what I have just wrote, then here is a simpler explanation
As we go down the group, the size of the atoms increases right? Thus the outer valence electron goes farther away from the nucleus (the nucleus is at the center). Metallic bonding involves the attraction between the valence of electrons and the nucleus. Since the valence electrons are farther away, there will be less attraction between the nucleus and the electrons. Kinda like a magnet and a strip of iron. The farther you take the strip from the magnet, the weaker the attraction. Since the attraction is weaker, less energy is required to overcome the forces of attraction.
If by any chance you don't get what I have just wrote, then here is a simpler explanation
As we go down the group, the size of the atoms increases right? Thus the outer valence electron goes farther away from the nucleus (the nucleus is at the center). Metallic bonding involves the attraction between the valence of electrons and the nucleus. Since the valence electrons are farther away, there will be less attraction between the nucleus and the electrons. Kinda like a magnet and a strip of iron. The farther you take the strip from the magnet, the weaker the attraction. Since the attraction is weaker, less energy is required to overcome the forces of attraction.