7 elements
Metalloids
Metalloids lie on the staircase line that divides metals from nonmetals. They look metallic but are brittle, and many are semiconductors — which is why silicon and germanium underpin modern electronics.
- Members
- 7
- At room temp
- 7 solid
- Melting range
- 254 to 2,075 °C
- Electronegativity
- 1.9 – 2.18
All metalloids
- 5BBoron10.81 u · 1808
- 14SiSilicon28.085 u · 1824
- 32GeGermanium72.63 u · 1886
- 33AsArsenic74.9216 u · c. 1250
- 51SbAntimony121.76 u · c. 3000 BCE
- 52TeTellurium127.6 u · 1782
- 84PoPolonium[209] u · 1898
On the borderline
Draw a staircase line from boron down to astatine on the periodic table and you separate the metals on the left from the nonmetals on the right. The elements along that line are metalloids. They look like metals, often shiny and grey, but they are brittle and shatter rather than bend, and chemically they behave more like nonmetals.
There is no single official list. Boron, silicon, germanium, arsenic, antimony and tellurium are almost always included. Polonium, which this site counts as a metalloid, and astatine are sometimes added, and some lists include carbon or selenium.
Semiconductors: the reason you can read this
Metals conduct electricity well and nonmetals barely at all. Metalloids sit in between, and the conductivity of silicon and germanium rises as they warm up or when tiny amounts of other elements are added. This property, semiconduction, can be controlled precisely.
Adding a little phosphorus or boron to ultra-pure silicon creates regions with extra or missing electrons. Placing those regions side by side makes diodes and transistors, the switches at the heart of every computer chip. The first transistor, in 1947, was made of germanium; silicon took over in the 1960s and gave Silicon Valley its name.
The members compared
Glass, alloys and poisons
Boron and silicon are the backbone of glass: ordinary glass is mostly silicon dioxide, and adding boron oxide makes heat-resistant borosilicate glass for laboratory and kitchen ware. Antimony hardens lead for batteries, and tellurium improves the machinability of steel and copper.
Arsenic is the metalloid with the darkest reputation. Its compounds were the poisoner’s favourite for centuries, and arsenic in groundwater still affects millions of people in South Asia. It also has legitimate uses, in some semiconductors and in a modern treatment for a type of leukaemia.
Frequently asked questions
How many metalloids are there?
Six elements are almost universally recognised: boron, silicon, germanium, arsenic, antimony and tellurium. Depending on the source, polonium, astatine, carbon, aluminium or selenium may also be counted; this site includes polonium, making seven.
Is silicon a metal?
No. Silicon looks metallic and conducts some electricity, but it is brittle and forms acidic oxides like a nonmetal. It is classed as a metalloid.
Why are metalloids used in electronics?
Their electrical conductivity sits between that of metals and insulators and can be tuned by adding small amounts of other elements, which lets engineers build diodes, transistors and solar cells.