Question

the particle - level diagram above represents the structure of solid kf. although the molar mass of kcl is greater than that of kf, the density of kcl is actually less than that of kf. which of the following representations of the structure of kcl best helps to explain this phenomenon?

Explanation:

Step1: Recall density formula

Density $
ho=\frac{m}{V}$, where $m$ is mass and $V$ is volume. For ionic - solids, a lower density can be due to larger unit - cell volume.

Step2: Consider ionic radii

Chloride ion ($Cl^-$) has a larger ionic radius than fluoride ion ($F^-$). In $KCl$ and $KF$, the cations are the same ($K^+$). The larger $Cl^-$ ion will result in a larger unit - cell volume in $KCl$ compared to $KF$.

Step3: Analyze the impact on density

Since density is mass per unit volume, with a larger volume for $KCl$ (even though it has a greater molar mass) and assuming similar packing efficiencies, the density of $KCl$ is lower. A particle - level diagram showing larger spaces between ions in $KCl$ compared to $KF$ would best explain this.

Answer:

A diagram with larger inter - ionic distances in $KCl$ compared to $KF$ would best explain why the density of $KCl$ is less than that of $KF$ despite its greater molar mass.