A period 3 element is one of the chemical elements in the third row (or period) of the 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 s-block of the periodic table, while the others are members of the p-block. All of the period 3 elements occur in nature and have at least one stable isotope.
Atomic structure In a quantum mechanical description of atomic structure, this period corresponds to the buildup of electrons in the third (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. This makes all eight elements analogs of the period 2 elements 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
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
… excerpt ends here. Continue reading the full article.
