SODIUM
Most metal ions emit light when
vaporized in a flame; this serves
as a qualitative way to identify
various ions. For sodium, a
characteristic yellow-orange color
is observed. Sodium vapor lamps
are often used in streetlighting.


Physical Properties

Atomic Number: 11
Atomic Weight: 22.98977
Electron Configuration: 1s22s22p63s1
First Ionization Energy: 496 kJ/mol
Crystal Structure: Body-Centered Cubic
Density: 0.97 g/cm3
Melting Point: 98oC
Atomic Radius: 186 pm
Ionic Radius: 97 pm
Standard Reduction Potential: -2.71 V (Na+ + e- = Na)

Occurence and Properties

Like the other alkali metals, sodium has a single valence electron. The chemistry of sodium is dominated by the tendency to lose this electron and form ionic bonds with nonmetals and polyatomic ions. Sodium occurs widely in nature and is found in the oceans, in salt lakes, and as deposits of solid sodium chloride. Metallic sodium is a soft enough to be cut with a knife. Freshly cut sodium has a distinctly metallic appearance. However, upon exposure to air, it quickly develops a white oxide coating. For this reason sodium is usually stored under mineral oil.

Reactions

Sodium reacts violently with water to produce sodium hydroxide and hydrogen gas. Sodium will also react with certain alcohols such as ethanol and metahnol to produce hydrogen gas. In the reaction with methanol, the product is sodium methoxide.

Na(s) + 2H2O(l) = 2NaOH(aq) + H2(g)
Na(s) + CH3OH(l) = CH3ONa + H2(g)

Sodium rapidly oxidizes in air. However, the usualy product is the peroxide rather then the oxide. Sodium will combine with sulfur to form sodium sulfide, but will not react with nitrogen.

4Na(s) + O2(g) = 2Na2O2(s)
2Na(s) + S(s) = Na2S(s)

Sodium combines readily with chlorine gas to give sodium chloride, or table salt. Similar reactions occur with the other members of the halogen family.

2Na(s) + Cl2(g) = 2NaCl(s)

Sodium metal combines with hydrogen to give the compound sodium hydride, which is a white ionic solid.

2Na(s) + H2(s) = 2NaH(s)

Preparation

Sodium cannot be prepared in a laboratory setting becasuse the reduction potential is much too high. Any attept to prepare sodium by the electrolysis of aqueous solutions always results in the reduction of water rather than reduction of the the sodium ion. Sodium is commercially prepared by the electrolysis of molten sodium chloride in what is called a downs cell; this cell employs a cylindrical iron cathode and graphite anode. The half-reactions that take place are shown below; sodium metal is produed at the cathode and chloride gas at the anode.. This reaction also serves as a method of producing chlorine gas.

2Na+(l) + 2e- = Na(l)
(reduction, anode half-reaction)
2Cl-(l) = Cl2(g) + 2e-
(oxidation, anode half-reaction)
2Na+(l) + 2Cl-(l) = 2Na(l) + Cl2(g)
overall reaction

Sodium Compounds

All sodium compounds are ionic compounds in which sodium is paired with a nonmetal or polyatomic ion. Most are white crystalline solids unless the anion itself is colored, as is the case with chromate and dichromate ions. Nearly all sodium compounds are soluble and sodium is often used as a spectator ion in a laboratory setting. Any general chemistry stockroom will contain a large number of sodium compounds. Several sodium compounds are important industrial chemicals, including sodium chloride, sodium hydrogen carbonate and sodium hydroxide. Sodium chloride is obtained from the mining of solid sodium chloride and from the evaporation of sea brines. It can be found in nearly every household as table salt. Industrially, it is also used in the manufacture of metallic sodium. Baking soda is sodium hydrogen carbonate. Some formulas and names of some common sodium compounds are listed below.

NaBr Sodium Bromide NaOH Sodium Hydroxide
Na2CO3 Sodium Carbonate NaI Sodium Iodide
NaCl Sodium Chloride NaNO2 Sodium Nitrite
Na2CrO4 Sodium Chromate NaNO3 Sodium Nitrate
Na2CrO7 Sodium Dichromate Na2O Sodium Oxide
NaHCO3 Sodium Hydrogen Carbonate Na2O2 Sodium Peroxide