Chemistry question

Question

In which pair of particles is the first member larger than the second member?

(A) Li + ; Be2+

(B) Li + ; Li

(C) Li + ; Na +

(D) Be; Mg

Could you explain which option is the correct answer

Answer 1

Answer: (A) Li⁺ is larger than Be²⁺

Explanation:

We begin with the periodic trend that atomic radius increases within a period going from right to left across the table, and it increases within a group going down the table. We next apply the fact that the cation is smaller than the neutral element since it has LOST an electron from the outer shell.

Comparing Li to Be, Li is to the left of Be so is larger, and Li⁺ and Be²⁺ are isoelectronic

Comparing L⁺ to Li, Li⁺ is smaller since it lost an electron

Comparing Li⁺ to Na⁺, Li is above Na so it is smaller

Comparing Be to Mg, Be is above Mg so it is smaller