Question

8-11.give the elemental symbol for the element with the greater
______ radius, potassium or calcium
______ radius, magnesium or magnesium cation
______ radius, chlorine or argon
______ radius, sulfur or sulfur anion

Explanation:

Step1: Compare potassium and calcium

Potassium (K) and calcium (Ca) are in the same period. Atomic radius decreases across a period. Potassium is in group 1 and calcium in group 2. So K has a larger radius.

Step2: Compare magnesium and magnesium cation

A cation is formed by losing electrons. The magnesium cation ($Mg^{2 + }$) has fewer electrons than magnesium (Mg). The out - most electrons in Mg are further from the nucleus, so Mg has a larger radius.

Step3: Compare chlorine and argon

Chlorine (Cl) and argon (Ar) are in the same period. Atomic radius generally decreases across a period. But argon is a noble gas and has a different way of measuring radius (van der Waals radius). However, in general trends, Cl has a larger atomic radius among them.

Step4: Compare sulfur and sulfur anion

An anion is formed by gaining electrons. The sulfur anion ($S^{2 - }$) has more electrons than sulfur (S). The extra electrons increase electron - electron repulsion, making the $S^{2 - }$ larger in radius.

Answer:

1. K
2. Mg
3. Cl
4. $S^{2 - }$