Fig. 4. Interpretation of the chemical bond.

After orbital preparation, strong interaction between radicals that have degenerate (or close) energy levels gives rise to electron pairing with frozen orbitals (ΔE_Cov, in green). This may or may not be accompanied by KE lowering as discussed in the text. Next, further energy lowering occurs by orbital mixing of the initial covalent state (green) with much higher states (pink). Such mixing has the effect of lowering the total energy (ΔE_Con, red) and contracting the electron density towards the atomic centers, as shown above the mixing diagrams (exaggerated for visual effect). This effect is significant for H–H and A–H bonds, but much less so for A–B bonds. Mixing with other unoccupied states (light blue) further lowers the energy via polarization and charge transfer (ΔE_PCT, black), which is significant for many A–B bonds¹⁹. While all of these terms are stabilizing in total energy, they may either increase or decrease the KE depending on the system (bottom pane).