Chapter 22, Problem 22.1VP

Interpretation Introduction

To find:

Which part of the Figure P22.1 best describes the increasing trend in monoatomic cation radii moving up or down a group or across a period in the periodic table?

Answer to Problem 22.1VP

Solution:

Figure P22.1 (d) best describes the increasing trend in the monoatomic cation radii moving down the group and across a period.

Explanation of Solution

The radius of a monoatomic cation decreases as we go across the period from left to right. Even though the size of the atomic nucleus increases with larger atomic number, moving across the period, the ionic and atomic sizes decrease. This is because the effective positive force of the nucleus also increases, drawing in the electrons more tightly. When the cation is formed, the entire valence shell is lost; thus, the outermost electrons in a cation are bound very closely to the nucleus, and hence the size of the cations decreases.

Hence, when the elements of the same period form cations, their size will increase as we go from the right to the left.

In Figure P21.1, we are given four figures from “a” to “d” of the periodic table depicting the trends in monoatomic radii for cations with the arrows such that the arrows point in the direction of increasing radii.

In Figure P22.1 (d), the monoatomic cation radii increase from the right to the left and from the top to the bottom. Thus, Figure P.22.1 (d) best describes the increasing trend in the monoatomic cation radii moving down the group and across a period.

Conclusion:

The radius of monoatomic cations increases as we move down the group and decrease as we move across the period.