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Nonmetal is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, every element in the periodic table can be termed either a metal or a non-metal. (A few elements with intermediate properties are referred to as metalloids.)
The elements generally regarded as nonmetals are:
- hydrogen (H)
- In Group 14: carbon (C)
- In Group 15 (the pnictogens): nitrogen (N), phosphorus (P)
- Several elements in Group 16, the chalcogens: oxygen (O), sulfur (S), selenium (Se)
- All elements in Group 17 - the halogens
- All elements in Group 18 - the noble gases
There is no rigorous definition for the term "nonmetal" - it covers a general spectrum of behaviour. Common properties considered characteristic of a nonmetal include:
- poor conductors of heat and electricity when compared to metals
- they form acidic oxides (whereas metals generally form basic oxides)
- in solid form, they are dull and brittle, rather than metals which are lustrous, ductile or malleable
- usually have lower densities than metals
- they have significantly lower melting points and boiling points than metals
- non-metals have high electronegativity
- nonmetals usually have little or no luster
Only eighteen elements in the periodic table are generally considered nonmetals, compared to over eighty metals, but nonmetals make up most of the crust, atmosphere and oceans of the earth. Bulk tissues of living organisms are composed almost entirely of nonmetals. Many nonmetals (hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine, and iodine) are diatomic, and most of the rest are polyatomic.
Nevertheless, even these 18 tend to become metallic at huge pressures.
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Chemical series of the periodic table |
The periodic table of the chemical elements is a tabular method of displaying the chemical elements.
Although precursors to this table exist, its invention is generally credited to Russian chemist Dmitri Mendeleev in 1869.
Mendeleev intended the table to illustrate recurring ('periodic') trends in the properties of the elements.
The layout of the table has been refined and extended over time, as new elements have been discovered, and new theoretical models have been developed to explain chemical behavior.
The periodic table is now ubiquitous within the academic discipline of chemistry, providing an extremely useful framework to classify, systematize and compare all the many different forms of chemical behavior.
The table has also found wide application in physics, biology, engineering, and industry. The current standard table contains 117 confirmed elements as of October 16, 2006 (while element 118 has been synthesized, element 117 has not).
- Arrangement
- Periodicity of chemical properties
- Structure of the periodic table
- History of the periodic table
- A list of who discovered each element
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