Arrange the following elements from greatest to least tendency to accept an electron. Rank from greatest to least tendency to accept an electron. To rank items as equivalent, overlap them. Br Se Ge Ca K I arranged this in the order i listed above and was told it was the incorrect answer and Your answer shows the general trend, but there are some exceptions. For example, the tendency to gain an electron is lower than expected if a stable electron configuration is lost.

Br > Se > Ge > K> Ca

Explanation:

Generally in the periodic table, we know that electron affinity increases across a period. Electron affinity refers to the energy released when an extra electron is added to a neutral gaseous atom. Most times, the addition of an electron leads to the formation of a uninegative ion.

The sequence of decrease in electro affinity values appears to be consistent until we get to calcium and potassium. One would have ordinarily expected potassium to have a lower electron affinity than calcium. However, if potassium accepts an electron, that electron goes on to fill the 4s level. This process is more exothermic than in the case of calcium where the extra electron is added to the 3d level. The energy difference between the 4s and 3d levels is enough to make the process less exothermic (only 2.37KJmol-1) compared to that of potassium (48.4 KJmol-1). This explains the order of arrangement seen in the answer above.