NATURE OF MATERIALS - Materials for Civil and Construction Engineers - page 54

Subshell
s

p d f

1 2 3 4 5 6 7

Principal quantum number

FIGURE 2.2 Energy levels of electrons in different shells and subshels.

(e.g., the energy of subshell 1s is less than subshell 2s). Within a shell, the
energy level increases with the subshell location: Subshell f is a higher
energy state than subshell d, and so on. There is an energy overlap between
the shells: Subshell 4s is at a lower energy state than subshell 3d. The elec-
tron configuration, or structure of an atom, describes the manner in which
the electrons are located in the shells and subshells. The convention for
listing the location of shells in the atom is to list the quantum number, fol-
lowed by the subshell designation, followed by the number of electrons in
the subshell raised to a superscript. This sequence is repeated for each sub-
shell that contains electrons. Table 2.2 provides some examples.

T ABLE 2.2 Sample Electron Configurations

Element Atomic Number Electron Configuration

1s 1 Hydrogen 1

1s 2

Helium 2

1s 2 2s 2 2p 2

Carbon 6

1s 2 2s 2 2p 6 Neon 10

1s 2 2s 2 2p 6 3s 1 Sodium 11

1s 2 2s 2 2p 6 3s 2 3p 1 Aluminum 13

1s 2 2s 2 2p 6 3s 2 3p 2

Silicon 14

1s 2 2s 2 2p 6 3s 2 3p 4

Sulfur 16

1s 2 2s 2 2p 6 3s 2 3p 6 Argon 18

1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 Calcium 20

1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 4s 1 Chromium 24

1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2

Iron 26

1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 1

Copper 29