The properties of form, appearance, and behaviour when mixed with metals are more like metals. Elasticity and general chemical behaviour are more like nonmetals.
Electrical conductivity, band structure, ionization energy, electronegativity, and oxides are intermediate between the two. Common applications[ edit ] The focus of this section is on the recognised metalloids.
Elements less often recognised as metalloids are ordinarily classified as either metals or nonmetals; some of these are included here for comparative purposes. Metalloids are too brittle to have any structural uses in their pure forms. Also shown are two silver pellets. Writing early in the history of intermetallic compounds , the British metallurgist Cecil Desch observed that "certain non-metallic elements are capable of forming compounds of distinctly metallic character with metals, and these elements may therefore enter into the composition of alloys".
He associated silicon, arsenic and tellurium, in particular, with the alloy-forming elements. Among the lighter metalloids, alloys with transition metals are well-represented. Alloys of silicon with iron and with aluminium are widely used by the steel and automotive industries, respectively.
Germanium forms many alloys, most importantly with the coinage metals. Arsenic can form alloys with metals, including platinum and copper ;  it is also added to copper and its alloys to improve corrosion resistance  and appears to confer the same benefit when added to magnesium.
The antileukaemic properties of white arsenic were first reported in Boron, silicon, arsenic and antimony have medical applications, and germanium and tellurium are thought to have potential. Boron is used in insecticides  and herbicides. Silicon is an essential trace element. In , arsenic trioxide under the trade name Trisenox was re-introduced for the treatment of acute promyelocytic leukaemia , a cancer of the blood and bone marrow.
Phosphorus, sulfur, zinc, selenium and iodine are essential nutrients, and aluminium, tin and lead may be. Sulfur is a constituent of sulfonamide drugs , still widely used for conditions such as acne and urinary tract infections. Bismuth is an ingredient in some antibacterials. Boron, in the form of borax , has been used as a textile flame retardant since at least the 18th century.