Question

The increasing order of the density of alkali metals is

• A. $Li < K < Na < Rb < Cs$
• B. $ Li < Na < K < Rb < Cs$
• C. $Cs < Rb < Na < K < Li$
• D. $Cs < Rb < K < Na < Li$
• E. $ Li < Na < Rb < K < Cs$

Answer 1

Answer: (A)

Due to their large size, the atoms of alkali metals are less closely packed. Consequently, have low density. On going down the group, both the atomic size and atomic mass increase but the increase in atomic mass compensates the bigger atomic size. As a result, the density of alkali metals increases from Li to Cs. Potassium is, however, lighter than sodium. It is probably due to an unusual increase in atomic size of potassium.