Atomic radius of potassium is greater than that of lithium.why?

The atomic radius of an atom is determined by the distance between the nucleus and the outermost electron shell. In the case of potassium and lithium, both elements have the same number of electron shells, but potassium has more electrons in its outermost shell compared to lithium.

Since potassium has more electrons in its outermost shell, the electrons experience greater repulsion from each other, causing the electron cloud to spread out further from the nucleus. This results in a larger atomic radius for potassium compared to lithium, which has fewer electrons in its outermost shell and a smaller atomic radius.

Atomic radii generally increase down a group in the periodic table. This is because, as we move down a group, additional electron shells are added to the atom. These additional electron shells increase the distance between the nucleus and the outermost electrons, resulting in an increase in atomic radius.

Potassium and lithium are both in Group 1 of the periodic table, which means they have one valence electron in their outermost shell. However, potassium is in the fourth period, while lithium is in the second period. Since potassium has more electron shells than lithium, the distance between the nucleus and the outermost electrons is greater in potassium. This results in a larger atomic radius for potassium compared to lithium.