partial replacement of calcium by magnesium in an origi-
nal limestone sediment. Is this explanation reasonable,
given what you know of the ionic radii of magnesium and
calcium ions?BUILDING YOUR KNOWLEDGE*88.Hydrogen can be obtained from water by electrolysis.
Hydrogen may someday be an important replacement
for current fuels. Describe some of the problems that
you would predict if hydrogen were used in today’s motor
vehicles.
*89.The only chemically stable ion of rubidium is Rb. The
most stable monatomic ion of bromine is Br. Krypton
(Kr) is among the least reactive of all elements. Compare
the electron configurations of Rb, Br, and Kr. Then pre-
dict the most stable monatomic ions of strontium (Sr) and
selenium (Se).
*90.The first ionization energy of potassium, K, is 419 kJ/mol.
What is the minimum frequency of light required to ion-
ize gaseous potassium atoms?
*91.Potassium and argon would be anomalies in a periodic table
in which elements are arranged in order of increasing
atomic weights. Identify two other elements among the
transition elements whose positions in the periodic table
would have been reversed in a “weight-sequence” arrange-
ment. Which pair of elements would most obviously be
out of place on the basis of their chemical behavior?
Explain your answer in terms of the current atomic model,
showing electron configurations for these elements.
*92.The second ionization energy for magnesium is 1451 kJ/
mol. How much energy, in kilojoules, must be absorbed by
1.50 g of gaseous magnesium atoms to convert them to
gaseous Mg^2 ions?(b) Butane burns in a limited amount of air to form car-
bon monoxide and water.
(c) When heated in the presence of very littleair, butane
“cracks” to form acetylene, C 2 H 2 ; carbon monoxide; and
hydrogen.
*81.(a) How much SO 2 would be formed by burning 1.00 kg
of bituminous coal that is 5.15% sulfur by mass? Assume
that all of the sulfur is converted to SO 2.
(b) If 27.0% of the SO 2 escaped into the atmosphere and
75.0% of the escaped SO 2 were converted to H 2 SO 4 , how
many grams of H 2 SO 4 would be produced in the atmo-
sphere?
*82.Write equations for the complete combustion of the
following compounds. Assume that sulfur is converted to
SO 2 and nitrogen is converted to NO. (a) C 6 H 5 NH 2 (),
(b) C 2 H 5 SH(), (c) C 7 H 10 NO 2 S().CONCEPTUAL EXERCISES*83.Write the electron configuration for the product of the sec-
ond ionization of the third largest alkaline earth metal.
*84.You are given the atomic radii of 110 pm, 118 pm, 120 pm,
122 pm, and 135 pm, but do not know to which element
(As, Ga, Ge, P, and Si) these values correspond. Which
must be the value of Ge?
*85.What compound will most likely form between potassium
and element X, if element X has the electronic configura-
tion 1s^22 s^22 p^63 s^23 p^4?
*86.Write the electron configurations of beryllium and
magnesium. What similarities in their chemical properties
can you predict on the basis of their electron configu-
rations?
*87.Dolostone is often more porous than limestone. One expla-
nation of the origin of dolostone is that it results from268 CHAPTER 6: Chemical Periodicity