Sodium

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This article is about the chemical element. For the nutrient commonly called "sodium", see salt. For the PlayStation Home game, see Sodium (PlayStation Home). For the racehorse, see Sodium (horse). For other uses of the word natrium, see Natrium (disambiguation).

Sodium,  ₁₁Na

Spectral lines of sodium
General properties
Name, symbol	sodium, Na
Pronunciation	/ˈsoʊdiəm/ SOH-dee-əm
Appearance	silvery white metallic
Sodium in the periodic table
Li ↑ Na ↓ K neon ← sodium → magnesium
Atomic number (Z)	11
Group, block	group 1 (alkali metals), s-block
Period	period 3
Element category	alkali metal
Standard atomic weight (±) (Ar)	22.98976928(2)[1]
Electron configuration	[Ne] 3s1
per shell	2, 8, 1
Physical properties
Phase	solid
Melting point	370.944 K ​(97.794 °C, ​208.029 °F)
Boiling point	1156.090 K ​(882.940 °C, ​1621.292 °F)
Density near r.t.	0.968 g/cm3
when liquid, at m.p.	0.927 g/cm3
Critical point	2573 K, 35 MPa (extrapolated)
Heat of fusion	2.60 kJ/mol
Heat of vaporization	97.42 kJ/mol
Molar heat capacity	28.230 J/(mol·K)
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 ​(a strongly basic oxide)
Electronegativity	Pauling scale: 0.93
Ionization energies	1st: 495.8 kJ/mol 2nd: 4562 kJ/mol 3rd: 6910.3 kJ/mol (more)
Atomic radius	empirical: 186 pm
Covalent radius	166±9 pm
Van der Waals radius	227 pm
Miscellanea
Crystal structure	​body-centered cubic (bcc)
Speed of sound thin rod	3200 m/s (at 20 °C)
Thermal expansion	71 µm/(m·K) (at 25 °C)
Thermal conductivity	142 W/(m·K)
Electrical resistivity	47.7 nΩ·m (at 20 °C)
Magnetic ordering	paramagnetic[2]
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 Number	7440-23-5
History
Discovery and first isolation	Humphry Davy (1807)
Most stable isotopes of sodium
iso NA half-life DM DE (MeV) DP 22Na trace 2.602 y β+→γ 0.5454 22Ne* 1.27453(2)[3] 22Ne ε→γ – 22Ne* 1.27453(2) 22Ne β+ 1.8200 22Ne 23Na 100% 23Na is stable with 12 neutrons
* = excited state
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Sodium /ˈsoʊdiəm/^[4] is a chemical element with symbol Na (from Greek Νάτριο) and atomic number 11. It is a soft, silver-white, highly reactive metal. In the Periodic table it is in column 1 (alkali metals), and like the other six elements in that column, it has a single electron in its outer shell that it readily donates, creating a positively charged atom—a cation. Its only stable isotope is ²³Na. The free metal does not occur in nature, but must be prepared from compounds. 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: sodium ions have been leached by the action of water from the Earth's minerals over eons; sodium and chlorine are the most common dissolved elements by weight in the oceans.
Sodium was first isolated by Humphry Davy in 1807 by the electrolysis of sodium hydroxide. Among many other useful sodium compounds, sodium hydroxide (lye) is used in soap manufacture, and sodium chloride (edible salt) is a de-icing agent and a nutrient for humans and cattle.
Sodium is an essential element for all animals and some plants. Sodium ions are the major cation in the extracellular fluid (ECF) and as such are the major contributor to the ECF osmotic pressure and ECF compartment volume. Loss of water from the ECF compartment increases the sodium concentration, a condition called hypernatremia. Isotonic loss of water and sodium from the ECF compartment decreases the size of that compartment in a condition called ECF hypovolemia.
By means of Na+/K+-ATPase, living human cells pump three sodium ions out of the cell in exchange for two potassium ions pumped in; comparing ion concentrations across the cell membrane, inside to outside, potassium measures about 40:1, and sodium, about 1:10. In nerve cells, the electrical charge across the cell membrane enables transmission of the nerve impulse—an action potential—when the charge is dissipated; sodium plays a key role in that activity.

Contents

• 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 oxidizes to grayish white unless immersed in oil or inert gas. Sodium can be easily cut with a knife and is a good conductor of electricity and heat. 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.^[5]
Sodium gas is at first green, then turns purple at higher temperatures.^[6]
In a flame test, sodium and its compounds glow yellow^[7] 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.^[8]

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. When 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.^[9] Like all the alkali metals, it reacts exothermically with water, and sufficiently large pieces melt to a sphere and may explode. The reaction produces caustic soda (sodium hydroxide) and flammable hydrogen gas. When burned in dry air, it forms primarily sodium peroxide with some sodium oxide. In moist air, it forms sodium hydroxide.^[10] Sodium metal is highly reducing, with the reduction of sodium ions requiring −2.71 volts,^[11] though potassium and lithium have even more negative potentials.^[12] Extracting sodium metal from a compound such as sodium chloride uses a significant amount of energy.^[10]

Isotopes

Main article: Isotopes of sodium

Twenty isotopes of sodium are known, but only ²³Na is stable. Two radioactive, cosmogenic isotopes are the byproduct of cosmic ray spallation: ²²Na has a half-life of 2.6 years and ²⁴Na, a half-life of 15 hours; all other isotopes have a half-life of less than one minute.^[13] Two nuclear isomers have been discovered, the longer-lived one being ^24mNa with a half-life of around 20.2 milliseconds. Acute neutron radiation, as from a nuclear critic

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Ditulis Unknown — Monday 25 July 2016 — 1 Comment — Kimia