Question

Periodic table trends: What is the trend in ionic radius across a period? Down a group? What is the trend in electronegativity across a period? Down a group? Using your knowledge of atomic structure, what is the explanation for this trend?

Answer 1

Ionic radius is defined as the internuclear distance between the center of the nucleus and the outermost electron in its shell. Along the groups, there is an addition of new shells that leads to increase in ionic radius. Electronegativity is defined as the tendency of an electron to attract towards itself. It decreases along the group due to the addition of extra shells.

Complete answer:
Elements arranged in a periodic table in vertical columns and horizontal rows. The vertical columns were known as groups and the horizontal rows were known as periods.
Ionic radius is the distance between the center of the nucleus and the outermost electron in its shell. In groups the atomic number increases and the incoming electron enters into new shell. Thus, the internuclear distance increases leads to increase in ionic radius down a group. In periods the electron enters into the same shell and has more nuclear attraction leads to decrease in ionic radius.
Electronegativity decreases along a group, as the increase in shells leads to lesser attraction of other atoms towards itself. Down a group. Electronegativity decreases and across a period, electronegativity increases.

Note:
The most electronegative element in the periodic table is fluorine it is in the ${2^{nd}}$ period and ${17^{th}}$ group, it is the last element in that period, and the first element in the group. Thus, it has more electronegativity. Though the last group inert gases exist, they do not attract any other atom due to stable configuration.