Chemistry · Ch 5 — Chemical Bonding
Interacting forces during covalent bond formation
Interacting forces during covalent bond formation
Bond formation lowers a system's total energy because of a changing balance between newly-arising attractive and repulsive forces as two atoms approach each other. When atoms with unpaired electrons of OPPOSITE spin draw close, new attractive forces appear (each atom's nucleus attracting the other atom's electron cloud) alongside new repulsive forces (nucleus-nucleus repulsion, and electron-electron repulsion); for hydrogen specifically, it is found experimentally that the newly-developed ATTRACTIVE forces outweigh the newly-developed repulsive ones, so the system's total potential energy steadily DECREASES as the two atoms approach. This fall in energy continues only up to a certain internuclear distance — the equilibrium (bond) distance — at which attraction and repulsion exactly balance and the system reaches its minimum possible energy; pushing the two nuclei any closer than this makes the repulsive forces dominate, so the potential energy rises again, sharply. If instead the two approaching atoms' unpaired electrons have PARALLEL (not opposite) spins, the potential energy of the system only ever INCREASES as th …
What this figure shows. A schematic of NH3 and H2O built from overlapping hybrid orbitals: in NH3, three of nitrogen's four hybrid orbitals each overlap axially with a hydrogen 1s orbital to form an N–H sigma bond, while the fourth orbital holds nitrogen's lone pair (not involved in bonding); in H2O, two of oxygen's four hybrid orbitals each overlap with a hydrogen 1s orbital to form an O–H sigma bond, while the remaining two orbitals each hold one of oxygen's two lone pairs. NOTE: the source PDF labels this figure 'Fig 5.1', duplicating the multiple-bonding figure number already used in section 5.2.3 for N2/CO2/C2H2 — an apparent misprint/extraction artifact in the original book, flagged rather than silently renumbered; the content described here (standard -hybrid-orbital pictures of NH3 and H2O) is independently well established regardless of the figure's corr …