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Non-metals are chemical elements that form simple elements with no metal-specific qualities. Non-metals typically include 22 elements: gases - hydrogen, nitrogen, oxygen, fluor, chlorine and inert gases; liquids - bromine; solids - boron, carbon, silicon, phosphorus, arsenic, sulphur, selenium, tellurium, iodine, astatine.
Only two non-metals - carbon and sulphur - were known in the antiquity. In 13th century arsenic was obtained, in 17th century hydrogen and phosphorus was discovered, in the end of 18th century - oxygen, nitrogen, chlorine, and tellurium. In 1789 À. L. Lavoisier included these non-metals in the list of simple substances (with the exception of chlorine, which was then accounted for as an oxygenized hydrochloric acid). In the first half of the 19th century bromine, iodine, selenium, silicon, and boron were obtained. It was possible to isolate fluor and discover inert gases only in the end of 19th century. Astatine was obtained artificially in 1940.
With the exception of the inert gases, which possess a very stable outermost electron shell and, therefore, are actually chemically not active, non-metals have high electro negativity. Non-metal atoms form simple anions (for example, Cl-, O2-) through attaching electrons or complex in combination with other elements (for example, ClO4-, SO42-, and PO43-).
Electro negativity of elements increases within the row from alkali metals to the right, and within subsets – from bottom to the top in the Mendeleev’s periodic table. Most electro negative are halogens – the elements of the VIIa subset; their electro negativity decreases from fluor to astatine. Non-metals form acidic oxides with oxygen, making acids after reacting with water; their strength decreases from VIIa subset to IVa subset. Elementary compounds of non-metals with hydrogen at room temperature are gaseous; water solutions of hydrogen compounds of the VIla subset are strong acids. Non-metal compounds with each other are marked by a covalent linkage, for example chlorine fluoride CIF, iodine chloride ICl, carbon disulphide CS2. In compounds of typical non-metals with metals the bonding is mostly ïî ïðåèìóùåñòâó ionic - for example, kalium chloride KCl, calcinated magnesium oxide MgO, aluminum three-bromide AlBr3. back |
