Question

The bond energies of $H-H$, $X-X$ and $H-X$ are $104,60$ and $102$ kcal/mole respectively. The electronegativity of hydrogen is $2.1$. The electronegativity of $X$ is:

• A. $2.5$
• B. $3.5$
• C. $3.0$
• D. $4.0$

Answer 1

The correct option is C $3.0$

$X_A-X_B=0.208\sqrt{\Delta }$

$\Delta =E_{H-X}-\frac{1}{2}[E_{H-H}+E_{X-X}]=102-0.5[104+60]$

$⟹\Delta =20$

$⟹X_A-X_B=0.208\sqrt{20}$

$⟹X_A-X_B=0.93$

$⟹X_A-2.1=0.93$

$X_A=0.93+2.1=3.03$