Explain the following, give appropriate reasons.
(i) Ionization potential of N is greater than that of O
(ii) First ionization potential of C-atom is greater than that of B-atom, where as the reverse is true for second ionization potential.
(iii) The electron affinity values of Be and Mg are almost zero and those of N (0.02 eV) and P (0.80 eV) are very low
(iv) The formation of `F^(-)`. (g) from F(g) is exothermie while that of `O^(2-)`(g) from O (g) is endothermic.

Explanation

(i) N(Z =7) `1s^2 2s^2 2p_x^1 2p_y^1 2p_z^1`. It has exactly half filled electronic configuration and it is more stable. Due to stability, ionization energy of nitrogen is high.
`O (Z =8) 1s^2 2s^2 2p_x^2 2p_y^1 2p_z^1`. It has incomplete electronic configuration and it requires less ionization energy.
`IE_1NgtI.E_1O`
(ii) C(Z=6) `1s^2 2s^2 2p_x^1 2p_y^1`. 1. The electron removal from p orbital is very difficult. So carbon has highest first ionization potential.
B `(Z=5) 1s^2 2s^2 2p^1`. In boron nuclear charge is less than that of carbon, so boron has lowest first ionization potential.
`I.E_1 CgtI.E_1 B` But it is reverse in the case of second ionization energy. Because in case of B the electronic configuration is `1s^2 2s^2`, which is completely filled and it has high ionization energy. But in C the electronic configuration is `1s^2 2s^2 2p^1`, one electron removal is easy so it has low ionization energy.
`I.E_2BgtI.E_2C`
(iii) Be (Z =4) `1s^2 2s^2`
`Mg (Z-12) 1s^2 2s^2 2p^6 3s^2`
Noble gases has the electronic configuration of nsa np. All these are completely filled and are more stable. For all these elements Be, Mg and noble gases, addition of electron is unfavorable and so they have zero electron affinity.
Nitrogen `(Z =7) 1s^2 2s^2 2p_x^1 2p_y^1 2p_z^1`. It has halffilled electronic configuration. So addition of electron is unfavorable and it has very low electron affinity value of 0.02 eV. Phosphorus (Z = 15) `1s^2 2s^2 2p^6 3s^2 3p_x^1 3p_y^1 3p_z^1`. It also has half filled electronic configuration. Due to the symmetry and more stability, it has very low electron affinity value of 0.80 eV.
(iv)`F_((g)) +e^(-) to F_((g))^(-)` exothermic
F (Z = 9) `1s^2 2s^2 2p^5` . It is ready to gain one electron to attain the nearest inert gas configuration. By gaining one electron, energy is released, so it is an exothermic reaction.
`O_((g))+2e^(-) to O_((g))^(2-)`  endothermic
O (Z=8) `1s^(2) 2s^(2) 2p_(x)^(2), 2p_(y)^(1) 2p_(z)^(1)`. It is the small atom with high electron density. The first electron affinity is negative because energy is released in the process of adding one electron to the neutral oxygen atom. Second electron affinity is always endothermic (positive) because the electron is added to an ion which is already negative, therefore it must overcome the repulsion.