The amount of energy required to remove the most loosely bound electron from an isolated gaseous atom is called as first ionization energy `(IE_1)`.Similarly the amount of energies required to knock out second third etc. electrons from the isolated gaseous cation are called successive ionization energies and `IE_3gtIE_2gtIE_1`
(i)Nuclear charge (ii)Atomic size (iii)penetration effect of the electrons (iv)shielding effect of the inner electrons and (v)electronic configurations (exactly half filled & completely filled configurations are considered extra stable) affect the ionisation energies.
On the other hand, the amount of energy released when a neutral isolated gaseous atom accepts an extra electron to form gaseous anion is called electron affinity.
`O(g)+e^(-) overset("Exothermic")toO^(-)(g),DeltaH_(eg)=-141 kJ "mol"^(-1)`...(a)
`O^(-)(g)+e^(-)overset("Endothermic")to O^(2-)(g) , DeltaH_(eg)=+780 kJ "mol"^(-1)`...(b)
In (b) the energy has to be supplied for the addition of second electron due to electrostatic repulsion between an anion and extra electron (same charged species).The electron affinity of an element depends upon (i) atomic size (ii)nuclear charge & (iii)electronic configuration.In general, ionisation energy and electron affinity increases as the atomic radii decreases and nuclear charge increases across a period.In general in a group, ionisation energy and electron affinity decrease as the atomic size increases.
The members of third period have some higher (e.g. S and Cl) electron affinity values than the members of second period (e.g. O and F) because second period elements have very small atomic size.Hence there is a tendency of electron - electron repulsion, which results in less evolution of energy in the formation of corresponding anion.
Which one of the following statements is correct ?
A. The elements like F, Cl , Br etc having high values of electron affinity act as strong oxidising agent
B. The element having low values of ionisation energies act as strong reducing agent
C. The formation of `Be^(-)`(g) from Be (g) is an endothermic process
D. All of these
