Question

Which elements in the fourth period will have the lowest and highest electron affinities? Explain.

Answer 1

Electron affinity is the amount of energy released when an atom accepts an electron. In the periodic table, electron affinity increases from left to right in a period and decreases from top to bottom in a group. It is inversely proportional to the atomic radius of an atom.

• The third period consists of 18 electrons, namely- Potassium (K), Calcium (Ca), Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Gallium (Ga), Germanium (Ge), Arsenic (As), Selenium (Se), Bromine (Br), and Krypton (Kr).
• The element with completely filled valence shells has zero electron affinity. They don't need to complete the octet by adding any electron. The elements in the fourth period that have completely filled shells are Zinc and Krypton,
• The electronic configuration of Zinc is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{10}4{\mathrm{s}}^2$.
• The electronic configuration of Krypton is $1{\mathrm{s}}^{2}2{\mathrm{s}}^{2}2{\mathrm{p}}^{6}3{\mathrm{s}}^{2}3{\mathrm{p}}^{6}3{\mathrm{d}}^{10}4{\mathrm{s}}^{2}4{\mathrm{p}}^6$
• Also, halogens have the highest electron affinity in a period. Because of their smaller size, the electrons are held tightly.

Hence, in the fourth period:

1. The elements having the lowest electron affinity are Zinc and Krypton.
2. The element having the highest electron affinity is Bromine.