5.3.2.1: Orbital ionization energies
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To generate molecular orbital diagrams of heteronuclear diatomic molecules, we must start with a knowledge of the relative energies of electrons in different atomic orbitals. In other words, we need knowledge of the orbital potential energies (or orbital ionization energies).
There are two approaches you can use to "know" or estimate the atomic orbital energy levels.
Table \(\PageIndex{1}\): These are one-electron ionization energies of the valence orbitals calculated by average energies of both the ground-state and ionized-state configurations. (From Harry Gray, “ Electrons and Chemical Bonding ,” Benjamin, 1964, Appendix) Values are expressed in eV.
\[\begin{array} {|c|ccccccc|c|ccc|} \hline Atom & 1s & 2s & 2p & 3s & 3p & 4s & 4p & Atom & 3d & 4s & 4p \\ \hline H & -13.64 & & & & & & &Sc & -4.71 & -5.70 & -3.22 \\ He & -24.55 & & & & & & & Ti & -5.58 & -6.08 & -3.35 \\ Li & & -5.46 & & & & & & V & -6.32 & -6.32 & -3.47\\ Be & & -9.30 & & & & & & Cr & -7.19 & -6.57 & -3.47 \\ B & & -14.01 & -8.31 & & & & & Mn & -7.93 & -6.82 & -3.60 \\ C & & -19.47 & -10.66 & & & & & Fe & -8.68 & -7.07 & -3.72\\ N & & -25.54 & -13.14 & & & & & Ni & -10.04 & -7.56 & -3.84\\ O & & -32.36 & -15.87 & & & & & Cu & -10.66 & -7.69 & -3.97 \\ F & & -46.37 & -18.72 & & & & \\ Ne & & -48.48 & -21.57 & & & & \\ Na & & & & -5.21 & & & \\ Mg & & & & -7.69 & & & \\ Al & & & & -11.28 & -5.95 & & \\ Si & & & & -15.00 & -7.81 & & \\ P & & & & -18.72 & -10.17 & & \\ S & & & & -20.71 & -11.65 & & \\ Cl & & & & -25.29 & -13.76 & & \\ Ar & & & & -29.26 & -15.87 & & \\ K & & & & & & -4.34 & \\ Ca & & & & & & -6.08 & \\ Zn & & & & & & -9.42 & \\ Ga & & & & & & -12.65 & -5.95 \\ Ge & & & & & & -15.62 & -7.56 \\ As & & & & & & -17.61 & -9.05 \\ Se & & & & & & -20.83 & -10.79 \\ Br & & & & & & -24.05 & -12.52 \\ Kr & & & & & & -27.52 & -14.26 \\ \hline \end{array} \nonumber \]