any of the more than 100 known substances (of which 92 occur naturally) that cannot be separated into simpler substances and that singly or in combination constitute all matter

a metallic element having four allotropic forms; used in a wide variety of alloys; found in stibnite

a very poisonous metallic element that has three allotropic forms; arsenic and arsenic compounds are used as herbicides and insecticides and various alloys; found in arsenopyrite and orpiment and realgar

a highly unstable radioactive element (the heaviest of the halogen series); a decay product of uranium and thorium

a trivalent metalloid element; occurs both in a hard black crystal and in the form of a yellow or brown powder

a brittle grey crystalline element that is a semiconducting metalloid (resembling silicon) used in transistors; occurs in germanite and argyrodite