describe an sorbital as spherically symmetrical;that is, it is round like a basketball (Figure
5-21). The electron clouds (electron densities) associated with the 1s, 2s, and 3satomic
orbitals are shown just below the plots. The electron clouds are three-dimensional, and
only cross-sections are shown here. The regions shown in some figures (Figures 5-21
through 5-25) appear to have surfaces or skins only because they are arbitrarily “cut off”
so that there is a 90% probability of finding an electron occupying the orbital somewhere
within the surfaces.
Beginning with the second shell, each shell also contains a psubshell, defined by
- Each of these subshells consists of a set of three patomic orbitals, corresponding to the
three allowed values of m(1, 0, and 1) when 1. The sets are referred to as 2p,
3 p, 4p, 5p,... orbitals to indicate the main shells in which they are found. Each set of
atomic porbitals resembles three mutually perpendicular equal-arm dumbbells (see Figure
5-22). The nucleus defines the origin of a set of Cartesian coordinates with the usual x,
y, and zaxes (see Figure 5-23a). The subscript x, y, or zindicates the axis along which
each of the three two-lobed orbitals is directed. A set of three patomic orbitals may be
represented as in Figure 5-23b.
Beginning at the third shell, each shell also contains a third subshell (2) composed
of a set of five datomic orbitals (m2, 1, 0, 1, 2). They are designated 3d, 4d,
5 d,... to indicate the shell in which they are found. The shapes of the members of a set
are indicated in Figure 5-24.
In each of the fourth and larger shells, there is also a fourth subshell, containing a set
of seven fatomic orbitals (3, m3, 2, 1, 0, 1, 2, 3). These are shown in
Figure 5-25.
Thus, we see the first shell contains only the 1sorbital; the second shell contains the
2 sand three 2porbitals; the third shell contains the 3s, three 3p, and five 3dorbitals; and
the fourth shell consists of a 4s, three 4p, five 4d, and seven 4forbitals. All subsequent
shells contain s, p, d, and fsubshells as well as others that are not occupied in any presently
known elements in their lowest energy states.
Figure 5-21 The shape of an s
orbital.5-16 Atomic Orbitals 211See the Saunders Interactive
General Chemistry CD-ROM,
Screen 7.13, Shapes of Atomic Orbitals.xyzFigure 5-22 Three representations
of the shape of a porbital. The plot
at the bottom is along the axis of
maximum electron density for this
orbital. A plot along any other
direction would be different, because
a porbital is notspherically
symmetrical.xxr (^2) p^2 x