Semiconducting, not conducting
This is the defining property. Metals conduct better when cooled; metalloids conduct better when heated, doped or illuminated. That controllable, switchable conductivity is what makes a transistor possible.
The staircase elements that refuse to pick a side
Metalloids
Boron, silicon, germanium, arsenic, antimony and tellurium sit on the diagonal staircase that separates metals from nonmetals — and behave like both. They look metallic, conduct badly but not never, and one of them became the substrate of the entire digital age.
- Members
- 7
- Group
- Along the metal–nonmetal boundary
- Configuration
- p-block
- Radioactive
- 1
Highlighted in the periodic table
Every member
The 7 metalloids
5
B
Boron
10.81 u
A metalloid of extremes: harder than most metals, essential to plants, and the element that makes borosilicate glass survive a flame.
14
Si
Silicon
28.085 u
The element that turned sand into civilisation's substrate: every processor you have ever used is a slab of ultrapure silicon.
32
Ge
Germanium
72.64 u
The semiconductor that came first: the very first transistor was made of germanium, not silicon.
33
As
Arsenic
74.922 u
The classic poison of history — tasteless, undetectable for centuries, and still a groundwater crisis for millions.
51
Sb
Antimony
121.76 u
A brittle metalloid used since antiquity as eye cosmetic, and now as a flame retardant.
52
Te
Tellurium
127.6 u
Rare on Earth, common in the universe, and the element that makes rewritable optical discs work.
85
At
Astatine
210 u
The rarest naturally occurring element on Earth — perhaps 25 grams exist in the entire crust at any moment.
What defines them
Three things that make a metalloid
Metallic appearance, brittle reality
They are shiny and grey like metals, but they shatter rather than bend. Their bonding is covalent networks, not a delocalised electron sea.
Amphoteric chemistry
They form oxides that behave as acids in some reactions and bases in others, and they can appear as either the positive or negative partner in a compound.
Periodic trends
How they change across the family
Metallic character increases going down and to the left. Boron is the most nonmetallic; polonium (which some classifications include) is nearly a metal. The staircase itself is a boundary drawn on a gradient, so the membership list varies slightly between textbooks.
In the world
What they are used for
Silicon
Every integrated circuit ever made, plus solar cells, glass and silicone polymers. Semiconductor-grade silicon is refined to about one stray atom per billion.
Boron
Borosilicate glass that survives thermal shock, neutron-absorbing reactor control rods, and boron fibres in high-performance composites.
Germanium
The first transistor was germanium, not silicon. Today it is used for infrared optics, fibre-optic cores and high-speed GaAs-adjacent electronics.
Arsenic
Gallium arsenide semiconductors for high-frequency and optoelectronic devices; historically, pigments and pesticides.
Antimony
Flame retardants, lead-acid battery alloys, and — since it expands on freezing — the metal that made movable type fill its mould perfectly.
Tellurium
Cadmium telluride thin-film solar panels and the phase-change layer in rewritable optical discs.
Handling
Safety
Arsenic compounds are acutely and chronically toxic, and arsenic-contaminated groundwater affects tens of millions of people. Antimony and tellurium compounds are moderately toxic; tellurium exposure produces a persistent garlic odour on the breath. Crystalline silica dust causes silicosis. Elemental boron and silicon are essentially harmless.
Worth knowing
- Silicon is the second most abundant element in the Earth's crust, at about 28% by mass.
- Boron-10 absorbs neutrons so effectively that it is used both in reactor control rods and in experimental cancer therapy.
- Antimony sulfide was used as eye cosmetic — kohl — for at least five thousand years before anyone knew what an element was.
Common questions
About the metalloids
Which elements are actually metalloids?
Boron, silicon, germanium, arsenic, antimony and tellurium are on every list. Polonium and astatine appear on some. Selenium is sometimes included as a metalloid and sometimes as a nonmetal. There is no sharp boundary in nature, so there is no sharp boundary in the classification either.
Why is silicon used for chips instead of germanium?
Silicon forms a stable, insulating oxide layer — SiO₂ — simply by being exposed to oxygen. That native oxide is what makes the modern transistor gate possible, and germanium has no equivalent. Silicon is also abundant, cheap, and tolerates higher temperatures.
What makes a semiconductor different from a conductor?
A band gap. In a metal, electrons move freely into empty states at essentially zero energy cost. In a semiconductor there is a small gap that an electron must be given enough energy to cross — from heat, light, or an applied voltage. Because that gap can be tuned by doping, conduction can be switched on and off. That switch is a transistor.
Keep going
The other nine families
6
Alkali metals
Li Na K Rb Cs Fr
6
Alkaline earth metals
Be Mg Ca Sr Ba Ra
38
Transition metals
Sc Ti V Cr Mn Fe Co
12
Post-transition metals
Al Ga In Sn Tl Pb Bi
7
Nonmetals
H C N O P S Se
5
Halogens
F Cl Br I Ts
7
Noble gases
He Ne Ar Kr Xe Rn Og
15
Lanthanides
La Ce Pr Nd Pm Sm Eu
15
Actinides
Ac Th Pa U Np Pu Am