View source for Period 3 element

{{Short description|Third row of the periodic table}}
{{Morecite|date=March 2024}}
{{Periodic table (micro)| title=Period 3 in the [[periodic table]] | mark=Na,Mg,Al,Si,P,S,Cl,Ar}}
{{Sidebar periodic table|expanded=structure }}
A '''period 3 element''' is one of the [[chemical element]]s in the third row (or [[Periodic table period|period]]) of the [[periodic table|periodic 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 the [[Block (periodic table)#s-block|s-block]] of the periodic table, while the others are members of the [[Block (periodic table)#p-block|p-block]]. All of the period 3 elements occur in nature and have at least one [[stable isotope]].<ref><span class="plainlinks">[http://scienceaid.co.uk/chemistry/inorganic/period3.html Period 3 Element] {{Webarchive|url=https://web.archive.org/web/20120729193401/http://scienceaid.co.uk/chemistry/inorganic/period3.html |date=2012-07-29 }}</span> from Scienceaid.co.uk</ref>

== Atomic structure ==
In a [[quantum mechanics|quantum mechanical]] description of [[atomic structure]], this period corresponds to the buildup of electrons in the [[electron shell|third ({{math|1=''n'' = 3}}) shell]], more specifically filling its 3s and 3p subshells. There is a 3d subshell, but—in compliance with the [[Aufbau principle]]—it is not filled until [[period 4 element|period 4]]. This makes all eight elements analogs of the [[period&nbsp;2 element]]s in the same exact sequence. The [[octet rule]] generally applies to period 3 in the same way as to period 2 elements, because the 3d subshell is normally non-acting.

== Elements ==
{| class="wikitable floatright"
|+ Elements by number
|-
! scope="col" | [[Chemical element|Element]]
! scope="col" | {{abbr|#|Number}}
! scope="col" | Symbol
! scope="col" | [[Block (periodic table)|Block]]
! scope="col" | [[Electron configuration]]
|- style="background-color: {{element color|s-block}}"
! scope="row" | [[Sodium]]
| 11 || style="text-align: center" | Na || [[s-block]] || [Ne] 3s<sup>1</sup>
|- style="background-color: {{element color|s-block}}"
! scope="row" | [[Magnesium]]
| 12 || style="text-align: center" | Mg || [[s-block]] || [Ne] 3s<sup>2</sup>
|- style="background-color: {{element color|p-block}}"
! scope="row" | [[Aluminium]]
| 13 || style="text-align: center" | Al || [[p-block]] || [Ne] 3s<sup>2</sup> 3p<sup>1</sup>
|- style="background-color: {{element color|p-block}}"
! scope="row" | [[Silicon]]
| 14 || style="text-align: center" | Si || [[p-block]] || [Ne] 3s<sup>2</sup> 3p<sup>2</sup>
|- style="background-color: {{element color|p-block}}"
! scope="row" | [[Phosphorus]]
| 15 || style="text-align: center" | P || [[p-block]] || [Ne] 3s<sup>2</sup> 3p<sup>3</sup>
|- style="background-color: {{element color|p-block}}"
! scope="row" | [[Sulfur]]
| 16 || style="text-align: center" | S || [[p-block]] || [Ne] 3s<sup>2</sup> 3p<sup>4</sup>
|- style="background-color: {{element color|p-block}}"
! scope="row" | [[Chlorine]]
| 17 || style="text-align: center" | Cl || [[p-block]] || [Ne] 3s<sup>2</sup> 3p<sup>5</sup>
|- style="background-color: {{element color|p-block}}"
! scope="row" | [[Argon]]
| 18 || style="text-align: center" | Ar || [[p-block]] || [Ne] 3s<sup>2</sup> 3p<sup>6</sup>
|}

=== Sodium ===
{{Main|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 <sup>23</sup>Na. It is an abundant element that exists in numerous minerals such as [[feldspar]]s, [[sodalite]] and [[halite|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 [[soap]]making, 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 ===
{{Main|Magnesium}}
''Magnesium'' (symbol '''Mg''') is an [[alkaline earth metal]] and has common oxidation number +2. It is the eighth most [[abundance of the chemical elements|abundant element]] in the [[Earth's crust]]<ref name="Abundance">{{cite web |first=L. Bruce |last=Railsback |title=Abundance and form of the most abundant elements in Earth's continental crust |access-date=2008-02-15 |url=http://railsback.org/Fundamentals/ElementalAbundanceTableP.pdf |website=Some Fundamentals of Mineralogy and Geochemistry |archive-date=2011-09-27 |archive-url=https://web.archive.org/web/20110927064201/http://www.gly.uga.edu/railsback/Fundamentals/ElementalAbundanceTableP.pdf |url-status=live }}</ref> and the ninth in the known [[universe]] as a whole.<ref>{{Housecroft3rd|pages=305–306}}</ref><ref>{{cite book|last=Ash|first=Russell|title=The Top 10 of Everything 2006: The Ultimate Book of Lists|publisher=Dk Pub|year=2005|url=http://plymouthlibrary.org/faqelements.htm|isbn=0-7566-1321-3|url-status=dead|archive-url=https://web.archive.org/web/20100210170504/http://plymouthlibrary.org/faqelements.htm|archive-date=2010-02-10}}</ref> 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 (geology)|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]].<ref>{{cite news|url=http://www.seafriends.org.nz/oceano/seawater.htm#composition|title=The chemical composition of seawater|author=Anthoni, J Floor|year=2006}}</ref>

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 (chemistry)|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 [[alloy]]ing 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 water]]s.

=== Aluminium ===
{{Main|Aluminium}}
''Aluminium'' (symbol '''Al''') or ''aluminum'' ([[American and British English spelling differences#Different spellings for different pronunciations|American English]]) is a silvery white member of the [[boron group]] of [[chemical element]]s and a [[p-block metal]] classified by some chemists as a post-transition metal.<ref name=Huheey>Huheey JE, Keiter EA & Keiter RL 1993, ''Principles of Structure & Reactivity,'' 4th ed., HarperCollins College Publishers, {{ISBN|0-06-042995-X}}, p.&nbsp;28</ref> It is not soluble in water under normal circumstances. Aluminium is [[Abundance of elements in Earth's crust|the third most abundant element]] (after [[oxygen]] and [[silicon]]), and the [[element abundance|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 [[mineral]]s.<ref>{{cite web|publisher=Science is Fun|author=Shakhashiri, Bassam Z.|url=http://scifun.chem.wisc.edu/chemweek/Aluminum/ALUMINUM.html|title=Chemical of the Week: Aluminum|access-date=2007-08-28|archive-url=https://web.archive.org/web/20070906175512/http://scifun.chem.wisc.edu/CHEMWEEK/Aluminum/ALUMINUM.html|archive-date=2007-09-06|url-status=dead}}</ref> 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 (chemistry)|passivation]]. Structural components made from aluminium and its [[aluminium alloy|alloys]] are vital to the [[aerospace]] industry and are important in other areas of [[transport]]ation and structural materials. The most useful compounds of aluminium, at least on a weight basis, are the oxides and sulfates.

=== Silicon ===
{{Main|Silicon}}
''Silicon'' (symbol '''Si''') is a [[carbon group|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 {{langx|la|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 most [[Abundance of the chemical elements|common element]] in the universe by mass, but very rarely occurs as the pure free element in nature. It is most widely distributed in [[dust]]s, [[sand]]s, [[Minor planet|planetoids]] and [[planets]] as various forms of [[silicon dioxide]] (silica) or [[silicate]]s. Over 90% of the Earth's crust is composed of [[silicate minerals]], making silicon the [[Abundance of elements in Earth's crust|second most abundant element]] in the Earth's crust (about 28% by mass) after [[oxygen]].<ref>Nave, R. [http://hyperphysics.phy-astr.gsu.edu/hbase/tables/elabund.html Abundances of the Elements in the Earth's Crust], Georgia State University</ref>

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 [[clay]]s, silica [[sand]] and [[stone]]. Silica is used in ceramic [[brick]]. Silicate goes into [[Portland cement]] for [[mortar (masonry)|mortar]] and [[stucco]], and combined with silica sand and [[gravel]], to make [[concrete]]. Silicates are also in whiteware [[ceramic]]s 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 [[silicone]]s.

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 (< 10%) is perhaps even more critical. Because of wide use of silicon in [[integrated circuits]], the basis of most computers, a great deal of modern technology depends on it.

=== Phosphorus ===
{{Main|Phosphorus}}
''Phosphorus'' (symbol '''P''') is a [[Valency (chemistry)|multivalent]] [[Nonmetal (chemistry)|nonmetal]] of the [[pnictogen|nitrogen group]], phosphorus as a mineral is almost always present in its maximally oxidized ([[pentavalent]]) state, as inorganic [[phosphate minerals|phosphate rocks]]. Elemental phosphorus exists in two major forms—[[white phosphorus]] and [[red 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 to [[oxygen]] – hence its name given from Greek mythology, {{lang|el|Φωσφόρος}} meaning "light-bearer" (Latin: ''[[Lucifer]]''), referring to the "[[Hesperus|Morning Star]]", the planet [[Venus]]. 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 called [[chemiluminescence]]. It is also the lightest element to easily produce stable exceptions to the [[octet rule]].

The vast majority of phosphorus compounds are consumed as fertilizers. Other applications include the role of [[organophosphorus compound]]s in [[detergent]]s, [[pesticide]]s and [[nerve agents]] and [[match]]es.<ref>Herbert Diskowski, Thomas Hofmann "Phosphorus" in Ullmann's Encyclopedia of Industrial Chemistry 2005, Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a19_505}}</ref>

=== Sulfur ===
{{Main|Sulfur}}
''Sulfur'' (symbol '''S''') is an [[Abundance of the chemical elements|abundant]] [[Valence (chemistry)|multivalent]] nonmetal, one of [[chalcogen]]s. Under [[Standard temperature and pressure|normal conditions]], sulfur atoms form [[octasulfur|cyclic octatomic molecules]] with chemical formula S<sub>8</sub>. Elemental sulfur is a bright yellow [[crystal]]line solid when at room temperature. Chemically, sulfur can react as either an [[oxidant]] or a [[reducing agent]]. It oxidizes most [[metal]]s and several [[Nonmetal (chemistry)|nonmetal]]s, including carbon, which leads to its negative charge in most [[organosulfur compound]]s, 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]], [[History of China#Ancient China|China]] and [[ancient Egypt|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 language|English]], with this name still used in several nonscientific terms.<ref name=Greenwd>Greenwood, N. N.; & Earnshaw, A. (1997). Chemistry of the Elements (2nd Edn.), Oxford:Butterworth-Heinemann. {{ISBN|0-7506-3365-4}}.</ref> Sulfur was considered important enough to receive its own [[alchemical symbol]]. It was needed to make the best quality of [[gunpowder|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 dome]]s, 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 [[fertilizer]]s, 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 [[match]]es, [[insecticide]]s and [[fungicide]]s. 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 ===
{{Main|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 [[Abundance of elements in Earth's crust|second most abundant halogen and 21st most abundant element]] in Earth's crust. The great oxidizing power of chlorine led it to its [[Bleach (chemical)|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 pool]]s to keep them clean and [[swimming pool sanitation|sanitary]]. In the [[upper atmosphere]], chlorine-containing molecules such as [[chlorofluorocarbons]] have been implicated in [[ozone depletion]].

=== Argon ===
{{Main|Argon}}
''Argon'' (symbol '''Ar''') is the third element in group 18, the [[noble gas]]es. 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 language|Greek]] neuter adjective ''ἀργόν'', meaning "lazy" or "the inactive one", as the element undergoes almost no chemical reactions. The complete [[octet rule|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&nbsp;[[Kelvin|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 [[Ion laser#Argon laser|blue–green gas laser]].

== Biological roles ==

Sodium is an [[Dietary mineral|essential element]] for all animals and some plants. In animals, sodium ions are used against [[potassium]] ions to [[Na+/K+-ATPase|build 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 the [[human body]]; its ions are essential to all living [[Cell (biology)|cells]], where they play a major role in manipulating important biological [[polyphosphate]] compounds like [[Adenosine triphosphate|ATP]], [[DNA]], and [[RNA]]. Hundreds of [[enzyme]]s thus require magnesium ions to function. Magnesium is also the metallic ion at the center of [[chlorophyll]], and is thus a common additive to [[fertilizer]]s.<ref>{{cite web|url=http://www.mg12.info|title=Magnesium in health}}</ref> Magnesium compounds are used medicinally as common [[laxative]]s, antacids (e.g., [[milk of magnesia]]), and in a number of situations where stabilization of abnormal [[nerve]] excitation and blood vessel spasm is required (e.g., to treat [[eclampsia]]).

Despite its prevalence in the environment, [[aluminium salt]]s are not known to be used by any form of life. In keeping with its pervasiveness, it is well tolerated by plants and animals.<ref name=Ullmann>{{cite book |doi=10.1002/14356007.a01_527.pub2 |chapter=Aluminum Compounds, Inorganic|title=Ullmann's Encyclopedia of Industrial Chemistry|year=2007|last1=Helmboldt|first1=Otto|last2=Keith Hudson|first2=L.|last3=Misra|first3=Chanakya|last4=Wefers|first4=Karl|last5=Heck|first5=Wolfgang|last6=Stark|first6=Hans|last7=Danner|first7=Max|last8=Rösch|first8=Norbert|isbn=978-3527306732}}</ref> 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,<ref name="Niels">{{cite journal|doi=10.1146/annurev.nu.04.070184.000321|pages =21–41|journal=Annual Review of Nutrition|volume=4|year=1984|title=Ultratrace Elements in Nutrition|first=Forrest H.|last=Nielsen|pmid=6087860}}</ref> though various [[sea sponges]] need silicon in order to have structure. It is much more important to the metabolism of plants, particularly many grasses, and [[silicic acid]] (a type of silica) forms the basis of the striking array of protective shells of the microscopic [[diatom]]s.

Phosphorus is essential for life. As phosphate, it is a component of [[DNA]], [[RNA]], [[Adenosine triphosphate|ATP]], and also the [[phospholipid]]s 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 of [[fertilizer]]s, 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 vitamins [[biotin]] and [[thiamine]], the latter being named for the Greek word for sulfur. Sulfur is an important part of many enzymes and in antioxidant molecules like [[glutathione]] and [[thioredoxin]]. Organically bonded sulfur is a component of all proteins, as the [[amino acid]]s [[cysteine]] and [[methionine]]. [[Disulfide]] bonds are largely responsible for the mechanical strength and insolubility of the protein [[keratin]], 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 a [[pulmonary agent]] in [[chemical warfare]]; however, chlorine is necessary to most forms of life, including humans, in the form of [[chloride]] ions.

Argon has no biological role. Like any gas besides oxygen, argon is an [[asphyxiant]].

== Table of elements ==
{{Periodic table (period 3)}}

== Notes ==
{{notelist}}

== References ==
{{reflist}}

{{Navbox periodic table}}
{{Periodic table (navbox)}}

{{DEFAULTSORT:Period 03}}
[[Category:Periods (periodic table)]]
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