NATURE OF MATERIALS - Materials for Civil and Construction Engineers - page 53

Distance from nucleus

Nucleus

FIGURE 2.1 Orbital path of model electrons.

Each orbital path, or shell, can hold only a fixed number of electrons.
The maximum number of electrons in a shell is equal to where n is the
principal quantum number of the shell. The orbital path of electrons is
defined by four parameters: the principal quantum number or shell desig-
nation, the subshell designation, the number of energy states of the subshell,
and the spin of the electron. Table 2.1 lists the number of electrons that can
be in each shell and subshell.
The energy level of an electron depends on its shell and subshell loca-
tion, as shown in Figure 2.2 (Callister 2003). Electrons always try to fill the
lowest energy location first. As shown in Figure 2.2, for a given subshell,
the larger the principal quantum number, the higher is the energy level

2n 2 ,

T ABLE 2.1 Number of Available Electron States in Some of the Electron Shells

and Subshells

Principal Number of Electrons

Quantum Shell Number of

Number Designation Subshell States per subshell per shell

1 K s 1 2 2

2 L s 1 2 8

p 3 6

3 M s 1 2 18

p 3 6

d 5 10

4 N s 1 2 32

p 3 6

d 5 10

f 7 14