Question

Arrange the elements in order from smallest to largest atomic radius.

a) Mg < Na < K
b) K < Mg < Na
c) Na < Mg < K
d) K < Na < Mg

Answer 1

The correct order of elements from smallest to largest atomic radius, considering periodic trends, is Magnesium (Mg), Sodium (Na), then Potassium (K). Atomic radius decreases across a period and increases down a group, hence option (a) Mg < Na < K is correct.

Step-by-step explanation:

To answer the student's question regarding the arrangement of elements from smallest to largest atomic radius, we must recall the periodic trends across periods and down groups (columns). In the periodic table, the atomic radius generally decreases across a period from left to right and increases down a group. This is due to the increasing number of protons which pull electrons closer to the nucleus across a period and due to the addition of electron shells as we move down a group.

Looking at the options provided:

• Magnesium (Mg) is to the right of Sodium (Na) in the same period, thus Mg has a smaller atomic radius.
• Potassium (K) is below Na in the same group, thus K has a larger atomic radius than both Mg and Na.

The correct order from smallest to largest atomic radius is therefore: Mg < Na < K, making option (a) the correct answer.