What will be the distance between H and Cl atom in HCl. The radius of hydrogen is $0.37\AA$ and the radius of chlorine is $1.67\AA$ ?

Bond length of single covalent bond  $=r_A+r_B-0.09\left(\Delta EN\right)$

Bond length $\left(d_{H-Cl}\right)=r_H+r_{Cl}-0.09\left(\Delta EN\right)$

$r_H=0.37\AA ;r_{Cl}=1.67\AA and\Delta EN=3.0-2.1=0.9$

$d_{H-Cl}=0.37+1.67-0.09\left(0.9\right)$  or, 

$d_{H-Cl}=2.04-0.08=1.96\AA$