General Chemistry Principles, Patterns, and Applications, 2011

character increases. Silicates contain anions that consist of only silicon and oxygen. Aluminosilicates are
formed by replacing some of the Si atoms in silicates by Al atoms; aluminosilicates with threedimensional
framework structures are called zeolites. Nitrides formed by reacting silicon or germanium
with nitrogen are strong, hard, and chemically inert. The hydrides become thermodynamically less stable
down the group. Moreover, as atomic size increases, multiple bonds between or to the group 14 elements
become weaker. Silicones, which contain an Si–O backbone and Si–C bonds, are high-molecular-mass
polymers whose properties depend on their compositions.
K E Y T A K E A W A Y
The group 14 elements show the greatest diversity in chemical behavior of any group;
covalent bond strengths decease with increasing atomic size, and ionization energies are
greater than expected, increasing from C to Pb.
C O N C E PTUAL P R OBLEMS
1. Why is the preferred oxidation state of lead +2 rather than +4? What do you expect the preferred oxidation
state of silicon to be based on its position in the periodic table?
2. Carbon uses pπ–pπ overlap to form compounds with multiple bonds, but silicon does not. Why? How does
this same phenomenon explain why the heavier elements in group 14 do not form catenated compounds?
3. Diamond is both an electrical insulator and an excellent thermal conductor. Explain this property in terms of
its bonding.
4. The lighter chalcogens (group 16) form π bonds with carbon. Does the strength of these π bonds increase or
decrease with increasing atomic number of the chalcogen? Why?
5. The heavier group 14 elements can form complexes that contain expanded coordination spheres. How does
this affect their reactivity compared with the reactivity of carbon? Is this a thermodynamic effect or a kinetic
effect? Explain your answer.
6. Refer to Table 22.2 "Selected Properties of the Group 14 Elements" for the values of the electron affinities of
the group 14 elements. Explain any discrepancies between these actual values and the expected values based
on usual periodic trends.
7. Except for carbon, the elements of group 14 can form five or six electron-pair bonds. What hybrid orbitals are
used to allow this expanded coordination? Why does carbon not form more than four electron-pair bonds?
8. Which of the group 14 elements is least stable in the +4 oxidation state? Why?
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