# Silicon and Group 14 Elements

Of course, the 4 bonds around the $$\ce{Si}$$ atoms point to the corners of a tetrahedron. These siloxane polymers are widely used as sealants, adhesives, additives, flame retardants, and lubricants. They have a wide application in industries. Depending on the organic group attached to silicon, the inorganic polymer Silicones has been an important class of materials.

## Questions

1. Which one lists the group 14 elements in order of increasing atomic weight?
1. $$\textrm{B Al Ga In Tl}$$
2. $$\textrm{C Si Ge Sn Pb}$$
3. $$\textrm{N P As Sb Bi}$$
4. $$\textrm{O S Se Te Po}$$
5. $$\textrm{F Cl Br I At}$$
2. Which allotrope of carbon is the hardest: diamond, graphite, or fullerenes?
3. What compound of carbon reacts with water to give acetylene gas?
4. When you want to extract silicon element, what do you use to reduce the sand: $$\ce{SiO2}$$, $$\ce{C}$$ or $$\ce{Mg}$$?
5. Which is stable towards air: methane or silane?
6. Give the name of polymers whose chains are held together by $$\ce{Si-O-Si}$$ bonds.
7. In the crystal structure of $$\ce{Si}$$, how many other $$\ce{Si}$$ atoms are connected to a particular $$\ce{Si}$$ atom?

## Solutions

Hint...
Knowing the groups of elements enables us to correlate their chemical properties. Each list of choices is a group of elements on the period table.
a = 3A, b = 14, c = 5A, d = 6A, e = 7A.
Hint...
Diamond is the hardest thing in the world. Fullerenes are large molecules consisting of 40 to hundreds of carbon atoms, with $$\mathrm{C_{60}}$$ being the most common.

3. Answer . . .$$\ce{CaC2}$$
Hint...
The reaction to produce acetylene gas is

$$\ce{CaC2 + H2O \rightarrow C2H2 + Ca(OH)2}$$

Acetylene is still an important industrial gas, as raw material for polymers.

4. Answer ...$$\ce{C}$$
Hint...
Carbon or coke is used for silicon metal, because $$\ce{Mg2Si}$$ is formed if $$\ce{Mg}$$ is used.

5. Answer ... methane is stable
Hint...
Methane is the major component of natural gas, and it will not react with air until ignited, whereas silane ignites explosively as soon as it contacts air.

Silicon and diamond have the same crystal structure. The edge of unit cells of $$\ce{Si}$$ is larger than that of diamond.