Question

For each of the following pairs of atoms, state which you expect to have the greater electron affinity:

(a) Xe or Cs;

(b) Pm or F;

(c) Ca or K;

(d) Po or At.

Short answer

The expected greater electron affinity of the elements in each pair is Cesium (Cs), Fluorine (F), Potassium (K), and Astatine (At), respectively

Step-by-step solution

Electron affinity.

The electron affinity of an element is the energy releasedwhen an electron enters the isolated gaseous neutral atom to form an anion.

The general representation is shown below.

${\text{M(g) +e}}^{-}\to {\text{M}}^{-}\text{(g)}$

a) Xenon (Xe) and Cesium (Cs).

Xenon element has a stable inert gas configuration and therefore does not allow any electron to enter the valence shell easily and if it happens then the amount of energy released is not much high (in order to remain stable).

Therefore,Cesium has a greater electron affinity.

b) Promethium (Pm) and Fluorine (F).

Electron affinity increases across a period and therefore, fluorine has got higher electron affinity compared to the Promethium element.

Fluorine easily takes an electron and achievesthe electronic configuration of inert gas; Neon.

${\text{F(g) +e}}^{-}\to {\text{F}}^{-}\left(g\right)$

Therefore,greater electron affinity is expected for Fluorine(F).

c) Calcium (Ca) and Potassium (K).

Potassium is an alkali metalwhereas calcium is an alkali earth metal. Potassium releases a greater amount of energy than calciumwhen an electron enters the isolated gaseous neutral atom.

Therefore,greater electron affinity is expected for Potassium(K) elements.

d) Polonium (Po) and Astatine (At).

Astatine element has got higher electron affinity compared to Polonium element. Because if astatine takes an electron, it attains the electronic configuration of inert gas Radon (Rn). Also, as electron affinity increases across a period, therefore Astatine has got higher electron affinity compared to polonium.

Here,greater electron affinity is expected for Astatine(At) element.