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Science and Society

Atomic Research
here are two types of scientific research: 1. J. J. Thomson investigates cathode rays.
QUESTIONS TO DISCUSS
Tbasic and applied. Basic research is 2. Robert Millikan measures the charge
driven by a search for understanding and of an electron. 1. Were the five research topics basic or
may or may not have practical applications.
3. Ernest Rutherford studies radioactive applied research?
Applied research has a goal of solving some
particles striking gold foil. 2. Would we ever have developed a
practical problem rather than just looking
4. Niels Bohr proposes a solar system model of the atom if all research had
for answers.
model of the atom by applying the to be practical?
Some people feel that all research should
quantum concept.
result in something practical, so all research
should be applied. Hold that thought while 5. Erwin Schrödinger proposes a model
considering if the following research dis- of the atom based on the wave nature
cussed in this chapter is basic or applied: of the electron.

and p sublevels. Th e n = 3 main energy level can have the z z z
s, p, and d sublevels. Finally, the n = 4 main energy level
can have all four sublevels, with s, p, d, and f. Th erefore,
the number of possible sublevels is the same as the
principal quantum number. y y y
The Bohr model considered the location of an electron x x x

as certain, like a tiny shrunken marble in an orbit. Th e
quantum mechanical model considers the electron as a A B C
wave, and knowledge of its location is very uncertain. Th e s orbitals: p orbitals: d orbitals:
Heisenberg uncertainty principle states that you cannot hold 2 electrons each of 3 pairs of each of 5 sets of
(outer orbitals of lobes holds 2 electrons lobes holds 2 electrons
measure the exact position of a wave because a wave
elements in groups = 6 electrons = 10 electrons
is spread out. One cannot specify the position and the IA and 2A of (outer orbitals of (found in elements
with atomic numbers of 21

momentum of a spread-out electron. The location of the the periodic table) groups IIIA to VIIIA)
and higher)
electron can only be described in terms of probabilities

of where it might be at a given instant. The probability of FIGURE 8.14 The general shapes of s, p, and d orbitals, the
location is described by a fuzzy region of space called an regions of space around the nuclei of atoms in which electrons are
likely to be found. (The f orbital is too difficult to depict.)
orbital. An orbital defines the space where an electron

is likely to be found. Orbitals have characteristic three-
dimensional shapes and sizes and are identifi ed with
electrons of characteristic energy levels. An orbital shape
represents where an electron could probably be located TABLE 8.2
at any particular instant. This “probability cloud” could

Quantum numbers and electron distribution to n = 4
likewise have any particular orientation in space, and the
direction of this orientation is uncertain. Maximum Maximum Number
3. Orientation in Space. An external magnetic fi eld applied Main Energy Energy Number of of Electrons per
Level Sublevels Electrons Main Energy Level

to an atom produces different energy levels that are related
to the orientation of the orbital to the magnetic fi eld. n = 1 s 2 2

The orientation of an orbital in space is described by the
n = 2 s 2
magnetic quantum number. This number is related to the

p 6 8
energies of orbitals as they are oriented in space relative to
n = 3 s 2
an external magnetic field, a kind of energy sub-sublevel. In

p 6
general, the lowest-energy sublevel (s) has only one orbital
orientation. The next higher-energy sublevel (p) can have d 10 18

three orbital orientations (Figure 8.14). The d sublevel can n = 4 s 2

have five orbital orientations, and the highest sublevel, f, p 6

can have a total of seven different orientations (Table 8.2). d 10
4. Direction of Spin. Detailed studies have shown that an f 14 32
electron spinning one way (say, clockwise) in an external
214 CHAPTER 8 Atoms and Periodic Properties 8-12