Answer
$K-F$ distance: $2.71$ angstroms
$Na-Cl$ distance: $2.83$ angstroms
$Na-Br$ distance: $2.98$ angstroms
$Li-Cl$ distance: $2.57$ angstroms
Work Step by Step
$KF$, $NaCl$, $NaBr$, $LiCl$
1) The ionic radii of the ions:
- $K^+$: 1.52 angstroms
- $F^-$: 1.19 angstroms
- $Na^+$: 1.16 angstroms
- $Cl^-$: 1.67 angstroms
- $Br^-$: 1.82 angstroms
- $Li^+$: 0.90 angstroms
2) To estimate cation-anion distance, we would sum the ionic radii of the two ions in each compound. In detail,
- $K-F$ distance: $1.52+1.19=2.71$ angstroms
- $Na-Cl$ distance: $1.16+1.67=2.83$ angstroms
- $Na-Br$ distance: $1.16+1.82=2.98$ angstroms
- $Li-Cl$ distance: $0.90+1.67=2.57$ angstroms