Z El. Electron Configuration^2 s+1Lj Ioniz. Pot.
1 H (1s)^2 S 1 / 2 13.6
2 He (1s)^21 S 0 24.6
3 Li He (2s)^2 S 1 / 2 5.4
4 Be He (2s)^21 S 0 9.3
5 B He (2s)^2 (2p)^2 P 1 / 2 8.3
6 C He (2s)^2 (2p)^23 P 0 11.3
7 N He (2s)^2 (2p)^34 S 3 / 2 14.5
8 O He (2s)^2 (2p)^43 P 2 13.6
9 F He (2s)^2 (2p)^52 P 3 / 2 17.4
10 Ne He (2s)^2 (2p)^61 S 0 21.6
11 Na Ne (3s)^2 S 1 / 2 5.1
12 Mg Ne (3s)^21 S 0 7.6
13 Al Ne (3s)^2 (3p)^2 P 1 / 2 6.0
14 Si Ne (3s)^2 (3p)^23 P 0 8.1
15 P Ne (3s)^2 (3p)^34 S 3 / 2 11.0
16 S Ne (3s)^2 (3p)^43 P 2 10.4
17 Cl Ne (3s)^2 (3p)^52 P 3 / 2 13.0
18 Ar Ne (3s)^2 (3p)^61 S 0 15.8
19 K Ar (4s)^2 S 1 / 2 4.3
20 Ca Ar (4s)^21 S 0 6.1
21 Sc Ar (4s)^2 (3d)^2 D 3 / 2 6.5
22 Ti Ar (4s)^2 (3d)^23 F 2 6.8
23 V Ar (4s)^2 (3d)^34 F 3 / 2 6.7
24 Cr Ar (4s)(3d)^57 S 3 6.7
25 Mn Ar (4s)^2 (3d)^56 S 3 / 2 7.4
26 Fe Ar (4s)^2 (3d)^65 D 4 7.9
36 Kr (Ar) (4s)^2 (3d)^10 (4p)^61 s 0 14.0
54 Xe (Kr) (5s)^2 (4d)^10 (5p)^61 s 0 12.1
86 Rn (Xe) (6s)^2 (4f)^14 (5d)^10 (6p)^61 s 0 10.7We see that the atomic shells fill up in the order 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d,
6p. The effect of screening increasing the energy of higherℓstates is clear. Its no wonder that the
periodic table is not completely periodic.
TheIonization Potentialcolumn gives the energy in eV needed to remove one electron from the
atom, essentially the Binding energy of the last electron. The Ionization Potential peaks for atoms
with closed shells, as the elctron gains binding energy from more positive charge in the the nucleus
without much penalty from repulsion of the other electrons in the shell. As charge is added to the
nucleus, the atom shrinks in size and becomes more tightly bound. A single electron outside a closed
shell often has the lowest Ionization Potential because it is well screened by the inner electrons. The
figure below shows a plot of ionization potential versus Z.