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Many-Electron Atoms 239

accordingly increase in energy with increasing l. This effect is illustrated in Fig. 7.8,

which is a plot of the binding energies of various atomic electrons as a function of

atomic number for the lighter elements.

Electrons that share a certain value of lin a shell are said to occupy the same

subshell.All the electrons in a subshell have almost identical energies, since the

dependence of electron energy upon mland msis comparatively minor.

The occupancy of the various subshells in an atom is usually expressed with the

help of the notation introduced in the previous chapter for the various quantum states

of the hydrogen atom. As indicated in Table 6.2, each subshell is identified by its prin-

cipal quantum number nfollowed by the letter corresponding to its orbital quantum

number l. A superscript after the letter indicates the number of electrons in that subshell.

For example, the electron configuration of sodium is written

1 s^22 s^22 p^63 s^1

which means that the 1s(n1, l0) and 2s(n2, l0) subshells contain two

electrons each, the 2p(n2, l1) subshell contains six electrons, and the 3s(n3,

l0) subshell contains one electron.

HBNFNe PCaMnZnBr

Atomic number

Electron binding energy, Ry

0.2

0.3

0.4

0.6

1

2

3

4

6

8

10

20

30

40

60

80

100

200

300

400

600

800

1000

0.8

10 15 20 25 30

1 s electron

2 s electron

2 p electron

3 s electron

3 p electron

3 d electron

4 s electron

4 p electron

He Be C O

5 35

Li

Figure 7.8The binding energies of atomic electrons in rydbergs. (1 Ry13.6 eVground-state

energy of H atom.)

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