One of a set of elements (around 20 in total) with certain physical and chemical properties opposite to those of metal
elements. The division between metal and non-metal elements forms the simplest division of the periodic table of the elements
. Common physical properties are that non-metals have low electrical conductivity, are brittle when solid, or are gases or liquids. Exceptions include graphite
, a form of carbon, which is a good electrical conductor.
In structure the non-metals are very diverse. Hydrogen
(Cl), and the noble gases (rare gases), helium
(Xe), and radioactive radon
(Rn), are gases. Only bromine
(Br) is a liquid at room temperature, and the rest are solids.
Non-metals are the chemical opposites of metals. Metals form positively charged ions or cations
; non-metals form negatively charged ions or anions
. The exceptions are the chemically unreactive noble gases (rare gases), although xenon does react under certain conditions. Non-metals are electronegative, which means that they are able to gain electrons when bonding with metals. Apart from the noble gases, the non-metal elements have incomplete outer electron shells, and so try to gain enough electrons to fill them. The noble gases do not react because they already have complete outer electron shells. The type of bonding where ions are formed is known as ionic bonding
. Non-metals may also share electrons with other non-metal elements to complete their outer shell; this type of bonding is known as covalent bonding
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