Page 441 - Schaum's Outline of Theory and Problems of Applied Physics

426 ATOMIC PHYSICS [CHAP. 34

Fig. 34-2

SOLVED PROBLEM 34.17

Why is a chlorine atom able to pick up only a single electron when it reacts chemically whereas an oxygen
atom can pick up two electrons?

A chlorine atom lacks one electron of a closed outer shell. When it picks up an electron, which it can do easily
because the other electrons in the outer shell do not shield the nuclear charge, this shell is closed, and any further
electrons would have to go into the next shell. However, an electron in the next shell would find a net charge of −e
inside its orbital, not a net charge of +7e as the electrons in the previous shell do, and hence would be repelled rather
than held to the atom. Since an oxygen atom lacks two electrons of a closed outer shell, it can accommodate two
additional electrons in this shell; further electrons would be repelled as in the case of a CI ion.
−

SOLVED PROBLEM 34.18
Why does a closed l = 2 subshell contain 10 electrons?
The possible values of the magnetic quantum number m l when the orbital quantum number isl = 2 are m l =−2,
1
−1, 0, +1, +2, which is a total of 5. An electron with a given value of m l can have m s =± , so the total number
2
of permitted quantum states in a d subshell is twice 5, or 10.

Multiple-Choice Questions

34.1. De Broglie waves can be regarded as waves of
(a) energy (c) electric charge
(b) momentum (d) probability

34.2. Wave behavior is exhibited by
(a) only particles at rest (c) only charged particles
(b) only moving particles (d) all particles
34.3. The velocity of the wave packet that corresponds to a moving particle is

(a) lower than the particle’s velocity
(b) equal to the particle’s velocity
(c) higher than the particle’s velocity
(d) may be any of the above
34.4. According to the uncertainty principle, it is impossible to precisely determine at the same time a particle’s
(a) position and charge (c) momentum and energy
(b) position and momentum (d) charge and mass

34.5. A hydrogen atom is in its ground state when its electron is
(a) at rest (c) in its lowest energy level
(b) inside the nucleus (d) in its highest energy level