Typical metalloids have a metallic appearance, but they are brittle and only fair conductors of electricity. Metalloids are usually too brittle to have any structural uses.They and their compounds are used in alloys, biological agents, catalysts, flame retardants, glasses, optical storage and optoelectronics, pyrotechnics, semiconductors, and electronics.
Metalloids usually look like metals but behave largely like nonmetals.
Physically, they are shiny, brittle solids with intermediate to relatively good electrical conductivity and the electronic band structure of a semimetal or semiconductor.
listed twelve (Emsley's plus boron, carbon, silicon, selenium, bismuth, polonium, moscovium and livermorium).
On average, seven elements are included in such lists; individual classification arrangements tend to share common ground and vary in the ill-defined used three criteria to describe the six elements commonly recognised as metalloids: metalloids have ionization energies around 200 kcal/mol (837 k J/mol) and electronegativity values close to 2.0.
The additional pull on outer electrons as nuclear charge increases generally outweighs the screening effect of having more electrons.
With some irregularities, atoms therefore become smaller, ionization energy increases, and there is a gradual change in character, across a period, from strongly metallic, to weakly metallic, to weakly nonmetallic, to strongly nonmetallic elements.
Going down a main group, the effect of increasing nuclear charge is generally outweighed by the effect of additional electrons being further away from the nucleus.
Atoms generally become larger, ionization energy falls, and metallic character increases.
Sporadically recognised elements show that the metalloid net is sometimes cast very widely; although they do not appear in the list of metalloid lists, isolated references to their designation as metalloids can be found in the literature (as cited in this article).
Metalloids lie on either side of the dividing line between metals and nonmetals.
A related effect can be seen in other diagonal similarities between some elements and their lower right neighbours, specifically lithium-magnesium, beryllium-aluminium, and boron-silicon.