Sodium Sodium (symbol
Na) is a soft, silvery-white, highly reactive metal and is a member of the
alkali metals; its only stable
isotope is 23Na. It is an abundant element that exists in numerous minerals such as
feldspars,
sodalite and
rock salt. Many salts of sodium are highly soluble in water and are thus present in significant quantities in the Earth's bodies of water, most abundantly in the oceans as
sodium chloride. Many sodium compounds are useful, such as sodium hydroxide (lye) for
soapmaking, and sodium chloride for use as a deicing agent and a nutrient. The same
ion is also a component of many minerals, such as
sodium nitrate. The free metal, elemental sodium, does not occur in nature but must be prepared from sodium compounds. Elemental sodium was first isolated by
Humphry Davy in 1807 by the
electrolysis of
sodium hydroxide.
Magnesium Magnesium (symbol
Mg) is an
alkaline earth metal and has common oxidation number +2. It is the eighth most
abundant element in the
Earth's crust and the ninth in the known
universe as a whole. Magnesium is the fourth most common element in the Earth as a whole (behind iron, oxygen and silicon), making up 13% of the planet's mass and a large fraction of the planet's
mantle. It is relatively abundant because it is easily built up in
supernova stars by sequential additions of three helium nuclei to carbon (which in turn is made from three helium nuclei). Due to the magnesium ion's high
solubility in water, it is the third most abundant element dissolved in
seawater. The free element (metal) is not found naturally on Earth, as it is highly reactive (though once produced, it is coated in a thin layer of oxide [see
passivation], which partly masks this reactivity). The free metal burns with a characteristic brilliant white light, making it a useful ingredient in flares. The metal is now mainly obtained by
electrolysis of magnesium salts obtained from
brine. Commercially, the chief use for the metal is as an
alloying agent to make
aluminium-magnesium alloys, sometimes called "
magnalium" or "magnelium". Since magnesium is less dense than aluminium, these alloys are prized for their relative lightness and strength. Magnesium ions are sour to the taste, and in low concentrations help to impart a natural tartness to fresh
mineral waters.
Aluminium Aluminium (symbol
Al) or
aluminum (
American English) is a silvery white member of the
boron group of
chemical elements and a
p-block metal classified by some chemists as a post-transition metal. It is not soluble in water under normal circumstances. Aluminium is
the third most abundant element (after
oxygen and
silicon), and the
most abundant metal, in the
Earth's crust. It makes up about 8% by weight of the Earth's solid surface. Aluminium metal is too reactive chemically to occur natively. Instead, it is found combined in over 270 different
minerals. The chief
ore of aluminium is
bauxite. Aluminium is remarkable for the metal's low
density and for its ability to resist
corrosion due to the phenomenon of
passivation. Structural components made from aluminium and its
alloys are vital to the
aerospace industry and are important in other areas of
transportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.
Silicon Silicon (symbol
Si) is a
group 14 metalloid. It is less reactive than its chemical analog
carbon, the nonmetal directly above it in the periodic table, but more reactive than
germanium, the metalloid directly below it in the table. Controversy about silicon's character dates from its discovery: silicon was first prepared and characterized in pure form in 1824, and given the name silicium (from , flints), with an
-ium word-ending to suggest a metal. However, its final name, suggested in 1831, reflects the more chemically similar elements carbon and boron. Silicon is the eighth most
common element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in
dusts,
sands,
planetoids and
planets as various forms of
silicon dioxide (silica) or
silicates. Over 90% of the Earth's crust is composed of
silicate minerals, making silicon the
second most abundant element in the Earth's crust (about 28% by mass) after
oxygen. Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building use of
clays, silica
sand and
stone. Silica is used in ceramic
brick. Silicate goes into
Portland cement for
mortar and
stucco, and combined with silica sand and
gravel, to make
concrete. Silicates are also in whiteware
ceramics such as
porcelain, and in traditional
quartz-based
soda–lime glass. More modern silicon compounds such as
silicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers called
silicones. Elemental silicon also has a large impact on the modern world economy. Although most free silicon is used in the steel refining, aluminum-casting, and fine chemical industries (often to make
fumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (8. Elemental sulfur is a bright yellow
crystalline solid when at room temperature. Chemically, sulfur can react as either an
oxidant or a
reducing agent. It oxidizes most
metals and several
nonmetals, including carbon, which leads to its negative charge in most
organosulfur compounds, but it reduces several strong oxidants, such as
oxygen and
fluorine. In nature, sulfur can be found as the pure element and as
sulfide and
sulfate minerals. Elemental sulfur crystals are commonly sought after by mineral collectors for their brightly colored
polyhedron shapes. Being abundant in native form, sulfur was known in ancient times, mentioned for its uses in
ancient Greece,
China and
Egypt. Sulfur fumes were used as fumigants, and sulfur-containing medicinal mixtures were used as balms and antiparasitics. Sulfur is referenced in the
Bible as
brimstone in
English, with this name still used in several nonscientific terms. Sulfur was considered important enough to receive its own
alchemical symbol. It was needed to make the best quality of
black gunpowder, and the bright yellow powder was hypothesized by alchemists to contain some of the properties of gold, which they sought to synthesize from it. In 1777,
Antoine Lavoisier helped convince the scientific community that sulfur was a basic element, rather than a compound. Elemental sulfur was once extracted from
salt domes, where it sometimes occurs in nearly pure form, but this method has been obsolete since the late 20th century. Today, almost all elemental sulfur is produced as a byproduct of removing sulfur-containing contaminants from
natural gas and
petroleum. The element's commercial uses are primarily in
fertilizers, because of the relatively high requirement of plants for it, and in the manufacture of
sulfuric acid, a primary industrial chemical. Other well-known uses for the element are in
matches,
insecticides and
fungicides. Many sulfur compounds are odiferous, and the smell of odorized natural gas, skunk scent, grapefruit, and garlic is due to sulfur compounds.
Hydrogen sulfide produced by living organisms imparts the characteristic odor to rotting eggs and other biological processes.
Chlorine Chlorine (symbol
Cl) is the second-lightest
halogen. The element forms diatomic molecules under
standard conditions, called dichlorine. It has the highest
electron affinity and the one of highest
electronegativity of all the elements; thus chlorine is a strong
oxidizing agent. The most common compound of chlorine, sodium chloride (
table salt), has been known since ancient times; however, around 1630, chlorine gas was obtained by the Belgian chemist and physician Jan Baptist van Helmont. The synthesis and characterization of elemental chlorine occurred in 1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated muriatic acid air", as he thought he synthesized the oxide obtained from the
hydrochloric acid, because acids were thought at the time to necessarily contain oxygen. A number of chemists, including Claude Berthollet, suggested that Scheele's "dephlogisticated muriatic acid air" must be a combination of oxygen and the yet undiscovered element, and Scheele named the supposed new element within this oxide as
muriaticum. The suggestion that this newly discovered gas was a simple element was made in 1809 by Joseph Louis Gay-Lussac and Louis-Jacques. This was confirmed in 1810 by
Sir Humphry Davy, who named it chlorine, from the Greek word
χλωρός (chlōros), meaning "green-yellow". Chlorine is a component of many other compounds. It is the
second most abundant halogen and 21st most abundant element in Earth's crust. The great oxidizing power of chlorine led it to its
bleaching and disinfectant uses, as well as being an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used in
swimming pools to keep them clean and
sanitary. In the
upper atmosphere, chlorine-containing molecules such as
chlorofluorocarbons have been implicated in
ozone depletion.
Argon Argon (symbol
Ar) is the third element in group 18, the
noble gases. Argon is the third most common gas in the
Earth's atmosphere, at 0.93%, making it more common than
carbon dioxide. Nearly all of this argon is
radiogenic argon-40 derived from the decay of
potassium-40 in the Earth's crust. In the universe,
argon-36 is by far the most common argon isotope, being the preferred argon isotope produced by
stellar nucleosynthesis. The name "argon" is derived from the
Greek neuter adjective
ἀργόν, meaning "lazy" or "the inactive one", as the element undergoes almost no chemical reactions. The complete
octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its
triple point temperature of 83.8058
K is a defining fixed point in the
International Temperature Scale of 1990. Argon is produced industrially by the
fractional distillation of
liquid air. Argon is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily non-reactive substances become reactive: for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. Argon gas also has uses in incandescent and fluorescent lighting, and other types of gas discharge tubes. Argon makes a distinctive
blue–green gas laser. == Biological roles ==