Why do first ionization energies decrease down group 7?
Let’s get this straight – Ionisation energies ALWAYS decrease down a group. That’s because it depends upon 3 factors: 1)Distance between nucleus & the valence electron 2)The positive charge on the nucleus (no. of protons) 3)The shilding effect of inner shell electrons As we go down the group, the no. of shells increase as does the distance between the valence electrons and the nucleus. Although the no. of protons increases down the group, attraction between the nucleus and valence electrons decreases due to the shielding effect of more electrons in filled inner shells and also due to the increased distance between them. So, you see no matter which group, ionisation energies always decreases down a group as it becomes easier to remove a valence elctron from an element at the bottom of a group than an element at the top.
