ElementsWhat are the metalloids?
The metalloids lie along a stair-step line between the metals and the nonmetals, and behave partly like each. They often look like metals but are brittle, and they carry electricity only moderately. That in-between behaviour makes silicon and germanium semiconductors, the base of all modern electronics. Books do not fully agree on which elements count as metalloids. This site follows the grouping used by PubChem.
The family in numbers
Melting points in this family run from 253.9 °C (polonium) to 2,075 °C (boron). Among its solid members, the least dense is silicon (2.33 g/cm³) and the densest is polonium (9.32 g/cm³). Known since ancient times: arsenic, antimony. The most recently discovered member is polonium (1898).
Semiconductors
A metal lets electricity through easily, and a nonmetal such as sulfur hardly at all. A metalloid such as silicon lies in between, and, more usefully, the amount it conducts can be controlled. Adding a tiny trace of another element, a step called doping, or changing the temperature or the light falling on it, changes how well it conducts. That control is the basis of the transistor, and billions of transistors on a wafer of silicon make a computer chip. Solar cells and LED lamps work on the same principle.
Where you meet them
Silicon is the second most abundant element in the Earth's crust, after oxygen. Sand and quartz are silicon dioxide, and glass is made from them. Boron is in borax and in heat-resistant borosilicate glass used for laboratory beakers and oven dishes. Germanium was used in the first transistors and is now used in fibre optics and night-vision lenses. Tellurium is used in some solar panels.
A warning
Arsenic and antimony are poisonous. Arsenic occurs naturally in the groundwater of some regions, including parts of West Bengal and Bangladesh, where water from deep tube wells has to be tested and treated.
All metalloids compared
| No. | Symbol | Name | Atomic mass | State | Melts at | Boils at | Density g/cm³ | Discovered |
|---|---|---|---|---|---|---|---|---|
| 5 | B | Boron | 10.81 | Solid | 2,075 °C | 4,000 °C | 2.37 | 1808 |
| 14 | Si | Silicon | 28.085 | Solid | 1,414 °C | 3,265 °C | 2.33 | 1824 |
| 32 | Ge | Germanium | 72.63 | Solid | 938.3 °C | 2,833 °C | 5.32 | 1886 |
| 33 | As | Arsenic | 74.92159 | Solid | 816.9 °C | 613.9 °C | 5.78 | Ancient |
| 51 | Sb | Antimony | 121.760 | Solid | 630.6 °C | 1,587 °C | 6.68 | Ancient |
| 52 | Te | Tellurium | 127.6 | Solid | 449.5 °C | 987.9 °C | 6.23 | 1782 |
| 84 | Po | Polonium | 208.98243 | Solid | 253.9 °C | 961.9 °C | 9.32 | 1898 |
Other families: alkali metals, alkaline earth metals, transition metals, post-transition metals, nonmetals, halogens, noble gases, lanthanides, actinides.