  We present an intuitive and general analytical approximation estimating the
energy of covalent single and double bonds between participating atoms in terms
of their respective nuclear charges with just three parameters, $[{E_\text{AB}
\approx a - b Z_\text{A} Z_\text{B} + c (Z_\text{A}^{7/3} +
Z_\text{B}^{7/3})}]$. The functional form of our expression models an
alchemical atomic energy decomposition between participating atoms A and B.
After calibration, reasonably accurate bond energy estimates are obtained for
hydrogen-saturated diatomics composed of $p$-block elements coming from the
same row $2\le n\le 4$ in the periodic table. Corresponding changes in bond
energies due to substitution of atom B by C can be obtained via simple
formulas. While being of different functional form and origin, our model is as
simple and accurate as Pauling's well-known electronegativity model. Analysis
indicates that the model's response in covalent bonding to variation in nuclear
charge is near-linear -- which is consistent with Hammett's equation.
