Question

give the reason : ionization potential decreases down the group .​

Answer 1

Ionization Potential:

The ability of an atom to loose an electron from the outer most shell(valence shell) when provided sufficient energy is known as I.P.

Now it is a common fact that in Periodic table, the elements are arranged in the order of increasing Atomic Number(Number of protons/electron for a neutral atom). Now if more protons are present, more space is required(simple explanation for easy imagination). Thus if more space is present, the size of atom actually increases. Now, another aspect to be noted here; all the electrons in all orbits are held tightly by the powerhouse(nucleus). Thus, for greater space(greater size), the nucleus has to hold every single electron by certain force(electrostatic force given by Coulomb, as charge on nucleus is positive due to protons, and on electrons the charge is negative). Thus for greater size, more electrons.would.be present and thus that certain force by the nucleus is distributed among all electrons. Now if the size is lesser, electrons would be less in.count, thus each electron would have greater part of force and they would he difficult to remove(thus I۔P increases as more energy would be required) and for greater sizes, electrons would be greater in count, thus that force will.he distributed among all electrons again and thus each electron would have a smaller.portion of that holding force(thus easy to be removed, hence I۔P decreases as lesser energy would be required). And obviously, as we move down the group, the atomic number increases and for that increased atomic number(proton/electrons for neutral atom) , the size will increase ultimately. Thus if we move down the group, atomic size will.increase, and due to increased size, the energy required will become less;thus, I۔P(Ionization potential) would be decreased.