PTL:Sodium

From ChemEd Collaborative

Sodium

Sodium, an alkali metal, is the first element of the 3rd period and so is in Group IA. Other members of the group are lithium (Li), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr).

Discovered

Sodium was first prepared by electrolysis of caustic soda, sodium hydroxide, in 1807 by Davy.

Name

The name is derived from soda, the substance from which the element was first obtained. The symbol Na is an abbreviation of natrum, Latin for sodium.

Characteristics

Sodium is present in fair abundance in the sun and stars. Sodium is the sixth most abundant element on earth, comprising about 2.6% of the earth's crust; it is the most abundant of the alkali group of metals of which it is a member.

Sodium metal has a body centered cubic structure.

Prepared

Sodium is now obtained commercially by the electrolysis of absolutely dry fused sodium chloride (the Downs process).

NaCl(liq) Na(liq) + ½ Cl₂(g)

This method is much cheaper than that of electrolyzing sodium hydroxide (the Castner process), as was used several years ago.

The most common compound is sodium chloride, but sodium occurs in many other minerals, such as soda niter (NaNO₃), cryolite (Na3AlF6), zeolite, and sodalite (Na₄Al₃(SiO₄)₃Cl). It is a very reactive element and is never found free in nature.

Minerals Containing Sodium

Cryolite

Zeolite

Reactions

Sodium is a soft, bright, silvery metal that floats on water, decomposing with the evolution of hydrogen and the formation of sodium hydroxide.

Na(s) + H₂O(liq) NaOH(aq) + ½ H₂(g)

It may or may not ignite spontaneously on water, depending on the amount of oxide and metal exposed to the water.

It also reacts with air to give sodium peroxide (Na₂O₂) and some oxide (Na₂O).

2 Na(s) + O₂(g) Na₂O₂(s)

Finally, it reacts violently with aqueous acids

2 Na(s) + 2 HCl(aq) 2 NaCl(aq) + H₂(g)

and aqueous bases, largely owing to the violent reaction of the metal with water.

Sodium should be treated with respect as it can be dangerous when improperly handled.

One reason for the vigorous reactivity of sodium is that it has the lowest ionization energy of the 3rd period elements.

Compounds

Metallic sodium is vital in the manufacture of sodamide (NaNH₂) and sodium cyanide (NaCN), sodium peroxide (Na₂O₂), and sodium hydride (NaH). It is used in preparing tetraethyl lead, in the reduction of organic esters, and in the preparation of organic compounds. The metal may be used to improve the structure of certain alloys, to descale metal, to purify molten metals, and as a heat transfer agent. An alloy of sodium with potassium, NaK, is also an important heat transfer agent.

Uses

Ordinary table salt is sodium chloride; sodium is also important to the glass industry

Sodium is important to the petroleum industry; petroleum is used in the manufacture of a number of products

Sodium compounds are important to the paper, [glass], soap, textile, [petroleum], chemical and metal industries. Soap is generally a sodium salt of certain fatty acids.

Important compounds containing sodium are: borax; sodium bromide; sodium carbonate (washing soda) and [sodium hydrogen carbonate] (baking soda), both of which are produced in the Solvay process; sodium chlorate; [sodium chloride], or common salt; sodium cyanide; sodium aluminum fluoride, which appears in nature as cryolite; sodium nitrate, or Chile saltpeter; sodium phosphate; sodium silicate, which is a component of glass; sodium sulfate, known in medicine as Glauber's salt; and sodium sulfide.

Sodium vapor lamps, which generate bright yellow light (D lines) by applying high voltage to sodium in the gas phase, are used for lighting highways.

Emission Spectrum

This is the emission spectrum for sodium.