Sodium From Wikipedia, the free encyclopedia This article is about the chemical element. For the PlayStation Home game, see Sodium (PlayStation Home). For the racehorse, see Sodium (horse). "Natrium" redirects here. For the town in West Virginia, see Natrium, West Virginia. Page semi-protected Sodium 11Na ↑ Na ↓ K neon ← sodium → magnesium Sodium in the periodic table Appearance silvery white metallic Spectral lines of sodium General properties Name, symbol, number sodium, Na, 11 Pronunciation /ˈsoʊdiəm/ soh-dee-əm Element category alkali metal Group, period, block 1 (alkali metals), 3, s Standard atomic weight 22.98976928(2) Electron configuration [Ne] 3s1 2,8,1 Physical properties Phase solid Density (near r.t.) 0.968 g·cm−3 Liquid density at m.p. 0.927 g·cm−3 Melting point 370.944 K, 97.794 °C, 208.029 °F Boiling point 1156.090 K, 882.940 °C, 1621.292 °F Critical point (extrapolated) 2573 K, 35 MPa Heat of fusion 2.60 kJ·mol−1 Heat of vaporization 97.42 kJ·mol−1 Molar heat capacity 28.230 J·mol−1·K−1 Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 554 617 697 802 946 1153 Atomic properties Oxidation states 1, −1 (strongly basic oxide) Electronegativity 0.93 (Pauling scale) Ionization energies (more) 1st: 495.8 kJ·mol−1 2nd: 4562 kJ·mol−1 3rd: 6910.3 kJ·mol−1 Atomic radius 186 pm Covalent radius 166±9 pm Van der Waals radius 227 pm Miscellanea Crystal structure body-centered cubic Sodium has a body-centered cubic crystal structure Magnetic ordering paramagnetic[1] Electrical resistivity (20 °C) 47.7 nΩ·m Thermal conductivity 142 W·m−1·K−1 Thermal expansion (25 °C) 71 µm·m−1·K−1 Speed of sound (thin rod) (20 °C) 3200 m·s−1 Young's modulus 10 GPa Shear modulus 3.3 GPa Bulk modulus 6.3 GPa Mohs hardness 0.5 Brinell hardness 0.69 MPa CAS registry number 7440-23-5 History Discovery Humphry Davy (1807) First isolation Humphry Davy (1807) Most stable isotopes Main article: Isotopes of sodium iso NA half-life DM DE (MeV) DP 22Na trace 2.602 y β+→γ 0.5454 22Ne* 1.27453(2)[2] 22Ne ε→γ - 22Ne* 1.27453(2) 22Ne β+ 1.8200 22Ne 23Na 100% 23Na is stable with 12 neutrons * = excited state v t e · references Sodium is a chemical element with the symbol Na (from Latin: natrium) and atomic number 11. It is a soft, silver-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. The free metal does not occur in nature, but instead must be prepared from its compounds; it was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Sodium is the sixth most abundant element in the Earth's crust, and exists in numerous minerals such as feldspars, sodalite and rock salt (NaCl). Many salts of sodium are highly water-soluble, and their sodium has been leached by the action of water so that sodium and chlorine (Cl) are the most common dissolved elements by weight in the Earth's bodies of oceanic water. Many sodium compounds are useful, such as sodium hydroxide (lye) for soap-making, and sodium chloride for use as a de-icing agent and a nutrient (edible salt). Sodium is an essential element for all animals and some plants. In animals, sodium ions are used against potassium ions to build up charges on cell membranes, allowing transmission of nerve impulses when the charge is dissipated. The consequent need of animals for sodium causes it to be classified as a dietary inorganic macro-mineral. Contents [hide] 1 Characteristics 1.1 Physical 1.2 Chemical 1.3 Isotopes 1.4 Occurrence 2 Compounds 2.1 Aqueous solutions 2.2 Electrides and sodides 2.3 Organosodium compounds 3 History 4 Commercial production 5 Applications 5.1 Free element 5.1.1 Heat transfer 6 Biological role 7 Precautions 8 See also 9 References 10 External links Characteristics Physical Sodium at standard temperature and pressure is a soft, silvery metal that can be readily cut with a knife, and is a good conductor of electricity. These properties change dramatically at elevated pressures: at 1.5 Mbar, the color changes from silvery metallic to black; at 1.9 Mbar the material becomes transparent, with a red color; and at 3 Mbar sodium is a clear and transparent solid. All of these high-pressure allotropes are insulators and electrides.[3] When sodium or its compounds are introduced into a flame, they turn it yellow,[4] because the excited 3s electrons of sodium emit a photon when they fall from 3p to 3s; the wavelength of this photon corresponds to the D line at 589.3 nm. Spin-orbit interactions involving the electron in the 3p orbital split the D line into two; hyperfine structures involving both orbitals cause many more lines.[5] Chemical Emission spectrum for sodium, showing the D line. A positive flame test for sodium has a bright yellow color. When freshly cut, sodium has a bright, silvery luster. If exposed to air, the surface rapidly tarnishes, darkening at first and then forming a white coating of sodium hydroxide and sodium carbonate. Sodium is generally less reactive than potassium and more reactive than lithium.[6] Like all the alkali metals, it reacts exothermically with water, to the point that sufficiently large pieces melt to a sphere and may explode; this reaction produces caustic sodium hydroxide and flammable hydrogen gas. When burned in dry air, it mainly forms sodium peroxide as well as some sodium oxide. In moist air, sodium hydroxide results.[7] Sodium metal is highly reducing, with the reduction of sodium ions requiring −2.71 volts.[8] Hence, the extraction of sodium metal from its compounds (such as with sodium chloride) uses a significant amount of energy.[7] However, potassium and lithium have even more negative potentials.[9] Isotopes Main article: Isotopes of sodium 20 isotopes of sodium are known, but only 23Na is stable. Two radioactive, cosmogenic isotopes are the byproduct of cosmic ray spallation: 22Na with a half-life of 2.6 years and 24Na with a half-life of 15 hours; all other isotopes have a half-life of less than one minute.[10] Two nuclear isomers have been discovered, the longer-lived one being 24mNa with a half-life of around 20.2 microseconds. Acute neutron radiation, such as from a nuclear criticality accident, converts some of the stable 23Na in human blood to 24Na; by measuring the concentration of 24Na in relation to 23Na, the neutron radiation dosage of the victim can be calculated.[11] Occurrence 23Na is created in the carbon-burning process in stars by fusing two carbon atoms together; this requires temperatures above 600 megakelvins and a star of at least three solar masses.[12] The Earth's crust contains 2.6% sodium by weight, making it the sixth most abundant element on Earth.[13] Because of its high reactivity, it is never found as a pure element. It is found in many different minerals, some very soluble, such as halite and natron, others much less soluble such as amphibole, and zeolite. The insolubility of certain sodium min