Page 73 - Theory and Problems of BEGINNING CHEMISTRY

62 ELECTRONIC CONFIGURATION OF THE ATOM [CHAP. 4

Alternatively, we can use the configuration of the previous noble gas, Ar, and add the extra electrons:
2
Co [Ar] 4s 3d 7
To determine the electronic configuration in this manner, start with the noble gas of the previous period and use
the subshell notation from only the period of the required element. Thus, for Co, the notation for Ar (the previous
2
7
noble gas) is included in the square brackets, and the 4s 3d is obtained across the fourth period. It is suggested
that you do not use this notation until you have mastered the full notation. Also, on examinations, use the full
notation unless the question or the instructor indicates that the shortened notation is acceptable.

Solved Problems

BOHR THEORY
4.1. Draw a picture of the electron jump corresponding to the third line in the visible emission spectrum of
hydrogen according to the Bohr theory.
Ans. In hydrogen, only jumps to or from the second orbit are in the visible region of the spectrum. The electron
falls from the fifth orbit to the second. The picture is shown as the third arrow of Fig. 4-3.

4.2. When electrons fall to lower energy levels, light is given off. What energy effect is expected when an
electron jumps to a higher-energy orbit?
Ans. Absorption of energy is expected. The energy may be light energy (of the same energies as are given off in
emission), or it may be heat or other types of energy.

4.3. What changes of orbit can the electron of hydrogen make in going from its fifth orbit to its ground state?

Ans. It can go from (a)5 → 4 → 3 → 2 → 1(b) 5 → 4 → 3 → 1(c)5 → 4 → 2 → 1
(d)5 → 4 → 1(e)5 → 3 → 2 → 1 ( f ) 5 → 3 → 1(g)5 → 2 → 1(h)5 → 1.

QUANTUM NUMBERS
4.4. What values are permitted for m l in an electron in which the l value is 0?
Ans. 0. (The value of m l may range from −0to +0; that is, it must be 0.)

4.5. Why must there be two electrons in an outer shell before the expansion of the next inner shell beyond
eight electrons?

Ans. The ns orbital must be filled before electrons enter the (n − 1)d orbitals in the shell below.
4.6. (a) In a football stadium, can two tickets have the same set of section, row, seat, and date? How many of
these must be different to have a legal situation? (b) In an atom, can two electrons have the same set of
n,l, m l , and m s ? How many of these must be different to have a “legal” situation?
Ans. (a) At least one of the four must be different (b) At least one of the four must be different

4.7. What are the possible values of m l for an electron with l = 4?
Ans. −4, −3, −2, −1, 0, +1, +2, +3, and + 4.

4.8. What are the permitted values of m s for an electron with n = 6,l = 4, and m l =−2?
1
1
Ans. m s =− or + , no matter what values the other quantum numbers have.
2 2