NOTE:
The common hydrogen atom contains one proton, one electron, and no
hydrogen.
2-4.
ORBITING ELECTRONS
The electrons revolve or orbit around the nucleus. They are arranged in shells or
orbits much like the planets revolve around the sun (see figure 2-2). The first shell (K
shell) can hold one or two electrons but no more. The second shell, or L shell, may
contain up to 8 electrons and the third, or M shell, may contain as many as 18 electrons.
Some atoms have numerous electrons. To determine the maximum number of
electrons in any given shell, the calculations in Table 2-1 can be used. However, no
outer shell actually contains more than eight electrons (see figure 2-3).
Figure 2-2. Diagram of K, L, and M shells.
2 X 12
=
2 (K shell)
2 X 22
=
8 (L shell)
2 X 32
=
18 (M shell)
NOTE:
Additional shells follow the same progression. For example, the N shell can
contain up to 32 (2 X 42 ) electrons.
Table 2-1. Determining the maximum number of electrons in any given shell.
MD0512
2-3