In terms of atomic structure, explain why the atomic radius of K is larger than that of Na

Explanation:

Sodium and potassium are present in group 1A. Both are alkali metals.

The atomic number of sodium is 11 and potassium is 19. Sodium is present in period 3rd while potassium is present in period 4th.

Electronic configuration of sodium:

Na₁₁ = 1s² 2s² 2p⁶ 3s¹

K₁₉ = 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

It can be seen in electronic configuration that in case of sodium the valance electron is present in third energy level while in case of K outer most  electron is present in 4th energy level. So atomic structure of sodium has three energy level and K has four energy  level that's why radius of potassium is greater than sodium because its the distance from center to outer most electronic shell.

Moreover as we move down the group atomic radii increased with increase of atomic number. The addition of electron in next level cause the atomic radii to increased. The hold of nucleus on valance shell become weaker because of shielding of electrons thus size of atom increased.

The atomic radius of K is larger than that of Na because K is below Na in the periodic table.

The atomic radius of an element is the distance from the center of an atom to the outermost shell of the electron.

Atomic radius decreases across the period because valence electrons are being added while atomic radius increases down the group because the number of energy levels (n) increases  and hence the distance between the nucleus and the outermost orbital.

Since K is below Na in group 1, we can conclude that the atomic radius of K is larger than that of Na.

Learn more on atomic radius at link.

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