Chapter 6, Problem 71A

Interpretation Introduction

Interpretation:

A decrease in density across the period from potassium to chromium is to be explained.

Concept Introduction :

Periodic trends are patterns found in the periodic table that show several facets of a particular element. A periodic trend is observed in atomic size also. Atomic size increases down the group. Whereas atomic size decreases across the period or decreases from left to right.

Answer to Problem 71A

Density changes inversely with volume.

Explanation of Solution

The formula for the calculation of density is as follows:

  $\text{Density}=\frac{\text{mass}}{\text{volume}}$

So, density changes inversely with volume. Volume is directly proportional to the size of the atom and the atomic size decreases across the period or decreases from left to right. This is because when moving left to right in the periodic table, the number of shells stays constant while the nuclear charge increases by one at each step. As nuclear charge increases, electrons in the outermost shell are drawn to it with increasing force, which causes the size of atoms to gradually shrink over time.

Thus, density increases across the period from potassium and chromium.