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Aperiod 3 element is one of thechemical elements in the third row (orperiod) of theperiodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases: a new row is begun when chemical behavior begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine and argon. The first two, sodium and magnesium, are members of thes-block of the periodic table, while the others are members of thep-block. All of the period 3 elements occur in nature and have at least onestable isotope.[1]
In aquantum mechanical description ofatomic structure, this period corresponds to the buildup of electrons in thethird (n = 3) shell, more specifically filling its 3s and 3p subshells. There is a 3d subshell, but—in compliance with theAufbau principle—it is not filled untilperiod 4. This makes all eight elements analogs of theperiod 2 elements in the same exact sequence. Theoctet rule generally applies to period 3 in the same way as to period 2 elements, because the 3d subshell is normally non-acting.
| Element | # | Symbol | Block | Electron configuration |
|---|---|---|---|---|
| Sodium | 11 | Na | s-block | [Ne] 3s1 |
| Magnesium | 12 | Mg | s-block | [Ne] 3s2 |
| Aluminium | 13 | Al | p-block | [Ne] 3s2 3p1 |
| Silicon | 14 | Si | p-block | [Ne] 3s2 3p2 |
| Phosphorus | 15 | P | p-block | [Ne] 3s2 3p3 |
| Sulfur | 16 | S | p-block | [Ne] 3s2 3p4 |
| Chlorine | 17 | Cl | p-block | [Ne] 3s2 3p5 |
| Argon | 18 | Ar | p-block | [Ne] 3s2 3p6 |
Sodium (symbolNa) is a soft, silvery-white, highly reactive metal and is a member of thealkali metals; its only stableisotope is23Na. It is an abundant element that exists in numerous minerals such asfeldspars,sodalite androck 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 assodium chloride.
Many sodium compounds are useful, such as sodium hydroxide (lye) forsoapmaking, and sodium chloride for use as a deicing agent and a nutrient. The sameion is also a component of many minerals, such assodium nitrate.
The free metal, elemental sodium, does not occur in nature but must be prepared from sodium compounds. Elemental sodium was first isolated byHumphry Davy in 1807 by theelectrolysis ofsodium hydroxide.
Magnesium (symbolMg) is analkaline earth metal and has common oxidation number +2. It is the eighth mostabundant element in theEarth's crust[2] and the ninth in the knownuniverse as a whole.[3][4] 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'smantle. It is relatively abundant because it is easily built up insupernova 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 highsolubility in water, it is the third most abundant element dissolved inseawater.[5]
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 [seepassivation], 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 byelectrolysis of magnesium salts obtained frombrine. Commercially, the chief use for the metal is as analloying agent to makealuminium-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 freshmineral waters.
Aluminium (symbolAl) oraluminum (American English) is a silvery white member of theboron group ofchemical elements and ap-block metal classified by some chemists as a post-transition metal.[6] It is not soluble in water under normal circumstances. Aluminium isthe third most abundant element (afteroxygen andsilicon), and themost abundant metal, in theEarth'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 differentminerals.[7] The chiefore of aluminium isbauxite.
Aluminium is remarkable for the metal's lowdensity and for its ability to resistcorrosion due to the phenomenon ofpassivation. Structural components made from aluminium and itsalloys are vital to theaerospace industry and are important in other areas oftransportation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.
Silicon (symbolSi) is agroup 14metalloid. It is less reactive than its chemical analogcarbon, the nonmetal directly above it in the periodic table, but more reactive thangermanium, 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 (fromLatin:silicis, 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 mostcommon element in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed industs,sands,planetoids andplanets as various forms ofsilicon dioxide (silica) orsilicates. Over 90% of the Earth's crust is composed ofsilicate minerals, making silicon thesecond most abundant element in the Earth's crust (about 28% by mass) afteroxygen.[8]
Most silicon is used commercially without being separated, and indeed often with little processing of compounds from nature. These include direct industrial building use ofclays, silicasand andstone. Silica is used in ceramicbrick. Silicate goes intoPortland cement formortar andstucco, and combined with silica sand andgravel, to makeconcrete. Silicates are also in whitewareceramics such asporcelain, and in traditionalquartz-basedsoda–lime glass. More modern silicon compounds such assilicon carbide form abrasives and high-strength ceramics. Silicon is the basis of the ubiquitous synthetic silicon-based polymers calledsilicones.
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 makefumed silica), the relatively small portion of very highly purified silicon that is used in semiconductor electronics (< 10%) is perhaps even more critical. Because of wide use of silicon inintegrated circuits, the basis of most computers, a great deal of modern technology depends on it.
Phosphorus (symbolP) is amultivalentnonmetal of thenitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized (pentavalent) state, as inorganicphosphate rocks. Elemental phosphorus exists in two major forms—white phosphorus andred phosphorus—but due to its high reactivity, phosphorus is never found as a free element on Earth.
The first form of elemental phosphorus to be produced (white phosphorus, in 1669) emits a faint glow upon exposure tooxygen – hence its name given from Greek mythology,Φωσφόρος meaning "light-bearer" (Latin:Lucifer), referring to the "Morning Star", the planetVenus. Although the term "phosphorescence", meaning glow after illumination, derives from this property of phosphorus, the glow of phosphorus originates from oxidation of the white (but not red) phosphorus and should be calledchemiluminescence. It is also the lightest element to easily produce stable exceptions to theoctet rule.
The vast majority of phosphorus compounds are consumed as fertilizers. Other applications include the role oforganophosphorus compounds indetergents,pesticides andnerve agents andmatches.[9]
Sulfur (symbolS) is anabundantmultivalent nonmetal, one ofchalcogens. Undernormal conditions, sulfur atoms formcyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellowcrystalline solid when at room temperature. Chemically, sulfur can react as either anoxidant or areducing agent. It oxidizes mostmetals and severalnonmetals, including carbon, which leads to its negative charge in mostorganosulfur compounds, but it reduces several strong oxidants, such asoxygen andfluorine.
In nature, sulfur can be found as the pure element and assulfide andsulfate minerals. Elemental sulfur crystals are commonly sought after by mineral collectors for their brightly coloredpolyhedron shapes. Being abundant in native form, sulfur was known in ancient times, mentioned for its uses inancient Greece,China andEgypt. Sulfur fumes were used as fumigants, and sulfur-containing medicinal mixtures were used as balms and antiparasitics. Sulfur is referenced in theBible asbrimstone inEnglish, with this name still used in several nonscientific terms.[10] Sulfur was considered important enough to receive its ownalchemical symbol. It was needed to make the best quality ofblack 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 fromsalt 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 fromnatural gas andpetroleum. The element's commercial uses are primarily infertilizers, because of the relatively high requirement of plants for it, and in the manufacture ofsulfuric acid, a primary industrial chemical. Other well-known uses for the element are inmatches,insecticides andfungicides. 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 (symbolCl) is the second-lightesthalogen. The element forms diatomic molecules understandard conditions, called dichlorine. It has the highestelectron affinity and the one of highestelectronegativity of all the elements; thus chlorine is a strongoxidizing 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 thehydrochloric 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 asmuriaticum. 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 bySir Humphry Davy, who named it chlorine, from the Greek wordχλωρός (chlōros), meaning "green-yellow".
Chlorine is a component of many other compounds. It is thesecond most abundant halogen and 21st most abundant element in Earth's crust. The great oxidizing power of chlorine led it to itsbleaching and disinfectant uses, as well as being an essential reagent in the chemical industry. As a common disinfectant, chlorine compounds are used inswimming pools to keep them clean andsanitary. In theupper atmosphere, chlorine-containing molecules such aschlorofluorocarbons have been implicated inozone depletion.
Argon (symbolAr) is the third element in group 18, thenoble gases. Argon is the third most common gas in theEarth's atmosphere, at 0.93%, making it more common thancarbon dioxide. Nearly all of this argon isradiogenicargon-40 derived from the decay ofpotassium-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 bystellar nucleosynthesis.
The name "argon" is derived from theGreek neuter adjectiveἀργόν, meaning "lazy" or "the inactive one", as the element undergoes almost no chemical reactions. The completeoctet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Itstriple point temperature of 83.8058 K is a defining fixed point in theInternational Temperature Scale of 1990.
Argon is produced industrially by thefractional distillation ofliquid 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 distinctiveblue–green gas laser.
Sodium is anessential element for all animals and some plants. In animals, sodium ions are used againstpotassium ions tobuild up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated; it is therefore classified as a dietary inorganic macromineral.
Magnesium is the eleventh most abundant element by mass in thehuman body; its ions are essential to all livingcells, where they play a major role in manipulating important biologicalpolyphosphate compounds likeATP,DNA, andRNA. Hundreds ofenzymes thus require magnesium ions to function. Magnesium is also the metallic ion at the center ofchlorophyll, and is thus a common additive tofertilizers.[11] Magnesium compounds are used medicinally as commonlaxatives, antacids (e.g.,milk of magnesia), and in a number of situations where stabilization of abnormalnerve excitation and blood vessel spasm is required (e.g., to treateclampsia).
Despite its prevalence in the environment,aluminium salts are not known to be used by any form of life. In keeping with its pervasiveness, it is well tolerated by plants and animals.[12] Because of their prevalence, potential beneficial (or otherwise) biological roles of aluminium compounds are of continuing interest.
Silicon is an essential element in biology, although only tiny traces of it appear to be required by animals,[13] though varioussea sponges need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses, andsilicic acid (a type of silica) forms the basis of the striking array of protective shells of the microscopicdiatoms.
Phosphorus is essential for life. As phosphate, it is a component ofDNA,RNA,ATP, and also thephospholipids that form all cell membranes. Demonstrating the link between phosphorus and life, elemental phosphorus was historically first isolated from human urine, and bone ash was an important early phosphate source. Phosphate minerals are fossils. Low phosphate levels are an important limit to growth in some aquatic systems. Today, the most important commercial use of phosphorus-based chemicals is the production offertilizers, to replace the phosphorus that plants remove from the soil.
Sulfur is an essential element for all life, and is widely used in biochemical processes. In metabolic reactions, sulfur compounds serve as both fuels and respiratory (oxygen-replacing) materials for simple organisms. Sulfur in organic form is present in the vitaminsbiotin andthiamine, the latter being named for the Greek word for sulfur. Sulfur is an important part of many enzymes and in antioxidant molecules likeglutathione andthioredoxin. Organically bonded sulfur is a component of all proteins, as theamino acidscysteine andmethionine.Disulfide bonds are largely responsible for the mechanical strength and insolubility of the proteinkeratin, found in outer skin, hair, and feathers, and the element contributes to their pungent odor when burned.
Elemental chlorine is extremely dangerous and poisonous for all lifeforms, and is used as apulmonary agent inchemical warfare; however, chlorine is necessary to most forms of life, including humans, in the form ofchloride ions.
Argon has no biological role. Like any gas besides oxygen, argon is anasphyxiant.
Period 3 in theperiodic table | ||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | |
| Group → | ||||||||||||||||||
| ↓ Period | ||||||||||||||||||
| 3 | Sodium11Na22.990 | Magnesium12Mg24.305 | Aluminium13Al26.982 | Silicon14Si28.085 | Phosphorus15P30.974 | Sulfur16S32.06 | Chlorine17Cl35.45 | Argon18Ar39.95 | ||||||||||
Primordial From decay Synthetic Border shows natural occurrence of the element | ||||||||||||||||||
