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All About Chemical element
A chemical element is a pure chemical substance consisting of a single type of atom distinguished by its atomic number, which is the number of protons in its atomic nucleus
Elements are divided into metals, metalloids, and non-metals
Familiar examples of elements are carbon, nitrogen, oxygen, silicon, arsenic, aluminium, iron, copper, gold, mercury, and lead.
The lightest chemical elements, including hydrogen, helium and smaller amounts of lithium, beryllium and boron, are thought to have been produced by various cosmic processes during the Big *** and cosmic-ray spallation
Production of heavier elements, from carbon to the very heaviest elements, proceeded by stellar nucleosynthesis, and these were made available for later solar system and planetary formation by planetary nebulae and supernovae, which blast these elements into space
The high abundance of oxygen, silicon, and iron on Earth reflects their common production in such stars
While most elements are generally stable, a small amount of natural transformation of one element to another also occurs in the decay of radioactive elements as well as other natural nuclear processes.
The history of the discovery and use of the elements began with primitive human societies that found native elements like copper and gold and extracted (smelted) iron and a few other metals from their ores
Alchemists and chemists subsequently identified many more, with nearly all of the naturally-occurring elements becoming known by 1900
The properties of the chemical elements are often summarized using the periodic table, which organizes the elements by increasing atomic number into rows ("periods") in which the columns ("groups") share recurring ("periodic") physical and chemical properties
Save for unstable radioactive elements with short half lives, all of the elements are available industrially, most of them in high degrees of purity.
Hydrogen and helium are by far the most abundant elements in the universe
However, iron is the most abundant element (by mass) making up the Earth, and oxygen is the most common element in Earth's crust
Although all known chemical matter is composed of these elements, chemical matter itself is hypothesized to constitute only about 15% of the matter in the universe
The remainder is believed to be dark matter, a range of substances whose composition is largely unknown and not composed of chemical elements, since it lacks protons, neutrons or electrons
Dark matter may also include normal baryonic matter and neutrinos.
When two or more distinct elements are chemically combined, with the atoms held together by chemical bonds, the result is termed a chemical compound
Two thirds of the chemical elements occur naturally on Earth only as compounds, and in the remaining third, often the compound forms of the element are most common
Chemical compounds may be composed of elements combined in exact whole-number ratios of atoms, as in water, table salt, and minerals such as quartz, calcite, and some ores
However, chemical bonding of many types of elements results in crystalline solids and metallic alloys for which exact chemical formulas do not exist
Relatively pure samples of isolated elements are uncommon in nature
While all of the 92 naturally occurring elements have been identified in mineral samples from Earth's crust, only a small minority of elements are found as recognizable, relatively pure minerals
Among the more common of such "native elements" are copper, silver, gold, carbon (as coal, graphite, or diamonds), sulfur, and mercury
All but a few of the most inert elements, such as noble gases and noble metals, are usually found on Earth in chemically combined form, as chemical compounds
While about 32 of the chemical elements occur on Earth in native uncombined forms, most of these occur as mixtures
For example, atmospheric air is primarily a mixture of nitrogen, oxygen, and argon, and native solid elements occur in alloys, such as that of iron and nickel.
As of November 2011, 118 elements have been identified, the latest being ununseptium in 2010
Of the 118 known elements, only the first 92 are known to occur naturally on Earth; 80 of them are stable, while the others are radioactive, decaying into lighter elements over various timescales from fractions of a second to billions of years
Those elements that do not occur naturally on Earth have been produced artificially as the synthetic products of nuclear reactions.