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Lesson: Chapter 3 — The Structure of Matter

3.6. Metals, non-metals and metalloids 9 of 10

Metalloids: silicon and boron

The elements lying along the staircase line have properties intermediate between metals and non-metals. Two of them are worth knowing well.

Silicon

Apart from oxygen, silicon is the element seen in the greatest quantity in the earth's crust.

Figure to be added

Figure 3.16: a lump of silicon, dark grey with a metallic sheen.
  • Silicon compounds exist in nature in crystalline and in amorphous forms.
  • Quartz and sand, and gems such as emerald, are crystalline silicon compounds. Clay is a compound containing silicon.
  • The melting point of silicon is 1410 °C.

Uses

  • Making transistors and diodes.
  • Making solar cells.
  • Making computer components.

Boron

Pure boron exists as a black, crystalline solid element.

Figure to be added

Figure 3.17: pieces of boron in a dish, dark and glassy.
  • Its density is 3300 kg m−3 and its melting point is 2200 °C.
  • Its reactivity is relatively low, so it does not react even when heated to high temperatures in air.
  • At very high temperatures, amorphous boron reacts with oxygen, nitrogen, nitric acid, concentrated sulphuric acid, carbon and sulphur, forming the corresponding compounds.

Uses

  • In welding metals.
  • Making skin ointments.
  • Producing glass that can be heated to high temperatures.