Electron affinity is a measure of an atom's ability to gain electrons. Predict the trend for electron affinity across a period. Explain your answer.

Answer: Electron affinity increases on moving across a period.

Explanation:

When an electron is added to a neutral atom to convert it into a negative ion, the tendency is known as electron affinity.

Smaller is the size of an atom more readily an electron will be gained by it because of strong force of attraction exerted by its nucleus towards the electron.

As moving from left to right in a period, more and more electrons get added up in the same shell and the attraction between the last electron and nucleus increases, which results in the shrinkage of size of an atom.

Also, size of atoms decreases from left to right in a periodic table, thus tendency to gain electrons will also increase on moving from left to right. So, on moving across a period, there will be an increase in electron affinity.