Question

1. “Ionic radius” is one of the more difficult trends as there is no distinct trend going across a period, only down a group. However, there are other smaller trends that are just as important.

   1. Compare the ions of Na, Mg, and Al. Fill in the following statement: “For _____________ ions in the same period, as the charge increases, the ionic radius _______________.” Explain this observation.

   2. Compare the ions of N, O, and F. Fill in the following statement: “For ______________ ions in the same period, as the charge increases, the ionic radius _______________.” Explain this observation.

Answer 1

1) For POSITIVE ions in the same period as charge increases ionic radii DECREASES.

This is because now more number of protons are holding number of electron.

for example in case of Al 3 + 13 protons are holding 10 electron while in case of Na+ 11 protons and holding 10 electron so effective nuclear charge will be higher in case of Al3+ ion thereby decreasing the overall size of the ion.

2) For NEGATIVE ions in the same period as charge increases ionic radii INCREASES.

This is because now more number of electrons are present as compared to Proton.

for example in case of N3- 7 protons are holding 10 electrons. so effective nuclear charge will be less which will result in more repulsion and thereby enhancing the size of the iron. while in case of F- Ion there is is 9 protons and 10 electrons so effective nuclear charge will be higher and hence comparatively smaller size would be there.