Chemistry 65.100 A, V
Midterm Test #1
October 2, 1998

Part A. Answer each question with a few sentences or equations where necessary. (5 Marks each)

1. State Hund’s rule.
2. What are the four quantum numbers? (name each, give the appropriate symbol, and give a brief description of each).
3. State how many valence electrons each of the following atoms have: B, Ti, C, Na, Kr
4. The electronic configuration of Curium (Cm) is [Rn]7s²5f ⁷6d¹. Why is it not [Rn]7s²5f ⁸ (which would be predicted from the orbital filling order)?
5. Why does ionization potential increase going from left to right across a period?
6. Write the complete electronic configuration (i.e. 1s² 2s² …..) of arsenic (As).

1. Lines in the Brackett series of the hydrogen spectrum come from transitions to the m=4 shell from higher shells.

(a) Calculate wavelength (in nm) of the highest energy transition in this series.
(b) In what portion of the electromagnetic spectrum is this line?
(c) Calculate the energy of the resulting photons in kJ/mol.

2. Tungsten (W) metal is produced by the reduction of the trioxide by hydrogen according to the (unbalanced) reaction:

WO_3(s) + H_2(g) à W_(s) + H₂O_(g)

(a) Balance the reaction
(b) Calculate how many grams of W can be obtained from 4.81 kg of WO_3(s) with an excess of hydrogen gas.

3. Arrange the following atoms in increasing order of radius and explain your reasoning: S, Cl, Ar, K, Ca

Some Useful Constants
N_av = 6.02 x 10²³ mol^-1
h = 6.63 x 10^-34 J s
c = 3.00 x 10⁸ m s^-1
R = 0.01097 nm^-1