22.2.2 Silicon

Question 1

Silicon

Answer 1

• Silicon used for semiconductors is nearly 100% purified through a series of processes.
• Silicates are a class of silicon compounds made from the tetrahedral SiO 44– anion.
• Silicones are a class of silicon compounds consisting of alternating silicon-oxygen chains with organic substituents on the silicon.

Question 2

note

Answer 2

• Silicon used for semiconductors is nearly 100% purified
  (about 10 –8 % impurities) through a series of processes.
• First, sand (SiO 2 ) is reduced to silicon (Si) at very high
  temperatures, using carbon as a reductant.
• The silicon is then reacted with chlorine gas (Cl 2 ) to produce silicon tetrachloride (SiCl 4 ), a low-boiling liquid that can then be purified by distillation.
• The silicon tetrachloride is then reacted with hydrogen gas (H 2 ), yielding solid silicon and hydrochloric acid (HCl).
• The silicon is further purified by zone refining. In zone
  refining, a piece of solid silicon (a boule) is passed through heating coils in an inert atmosphere. The impurities concentrate in the liquid portion, which causes all of the impurities to pass into one end. This end is then removed, leaving pure silicon.
• Silicates are a class of silicon compounds made from the tetrahedral SiO 44– anion.
• The two simplest silicates are the silicate ion (SiO 44– ) and the disilicate ion (Si 2 O 76– ).
• These ions can further polymerize to yield infinite chains ((SiO 3 ) x ), infinite sheets ((Si 2 O 5 ) x ), or infinite networks (SiO2).
• An example of a compound composed of infinite silicon
  sheets is talc (Mg 3 (Si 2 O 5 ) 2 (OH) 2 ). The sheets are held together only by dispersion forces, which allow them to slide over one another easily. This is why talc is slippery.
• Silicones are a class of silicon compounds consisting of chains of alternating silicon and oxygen atoms with organic substituents on the silicon.
• A silicone can be formed by reacting dichlorodimethylsilane ((CH 3 ) 2 Cl 2 Si) with water (H 2 O). The silicone formed is dimethylsiloxane.
• Different silicones are made by using hydrocarbons other than CH 3 as substituents, and by cross-linking the chains through the substituent groups.
• Examples of silicones include Silly Putty®, in which the
  chains are cross-linked, and bathtub caulking, in which the hydrocarbon substituents act to repel water.

Question 3

Which ion can be found between the silicate sheets of talc?

Answer 3

Mg2+

Question 4

Which of the following statements is false?

Answer 4

Talc is composed of one-dimensional silicone chains.

Question 5

Which percentage of the mass of the earth’s crust is composed of silicon?

Answer 5

27.7%

Question 6

In which dimension do infinite chains of disilicate anions form?

Answer 6

1

Question 7

Which of the following is commonly used to manufacture computer chips?

Answer 7

Silicon

Question 8

In the purification of silicon, what reductant is commonly used?

Answer 8

H2

Question 9

Which percentage of the mass of the earth’s crust is composed of oxygen?

Answer 9

46.4%

Question 10

Which characteristic do graphite and talc have in common?

Answer 10

Slipperiness

Question 11

What is the product resulting from the refining process of Si(s)?

Answer 11

SiCl4(l)

Question 12

Which of the following was used to develop the first transistor?

Answer 12

Germanium