Sodi­um is an el­e­ment in the 1ˢᵗ group of the 3ʳᵈ pe­ri­od of the Pe­ri­od­ic Ta­ble. It is in the sub­group of al­ka­line met­als; Na₂O sodi­um ox­ide and NaOH sodi­um hy­drox­ide dis­play typ­i­cal base prop­er­ties. The most im­por­tant nat­u­ral com­pounds of sodi­um are ta­ble salt NaCl, Glauber’s salt Na₂­SO₄·10H₂O and syl­van­ite NaCl·KCl.

Phys­i­cal prop­er­ties

Like oth­er al­ka­line met­als, sodi­um is a sil­very-white met­al. It is quite mal­leable and soft (metal­lic sodi­um can eas­i­ly be cut with a knife or scalpel, and a fresh cut shines in air). It has high elec­tro­con­duc­tiv­i­ty.

Ob­tain­ing sodi­um

There are sev­er­al meth­ods for ob­tain­ing metal­lic sodi­um:

• elec­trol­y­sis of a flux of sodi­um chlo­ride:

К(-): Na⁺ + 1e = Na⁰;

A(+): 2Cl⁻ – 2e = Cl₂⁰.

2Na­Cl = 2Na + Cl₂.

• ther­mal de­com­po­si­tion of sodi­um azide:

2NaN₃ = 2Na + 3N₂ (that salt is heat­ed to 250-300 ᵒC or 482-572 ᵒF);

• re­duc­tion of sodi­um car­bon­ate (the first known method of ob­tain­ing metal­lic sodi­um):

Na₂­CO₃ + 2C = 2Na + 3CO (re­ac­tion takes place with heat­ing to 1000 ᵒC (1832 ᵒF)).

At present, the main method for ob­tain­ing sodi­um is elec­trol­y­sis of flux­es of its salts (for ex­am­ple NaCl).

Chem­i­cal prop­er­ties of metal­lic sodi­um

Metal­lic sodi­um is usu­al­ly stored un­der a lay­er of kerosene, as it has high chem­i­cal re­ac­tiv­i­ty (Na can re­act vi­o­lent­ly with oxy­gen and air mois­ture even at room tem­per­a­ture). The pres­ence of sodi­um ions in a salt can be de­ter­mined by the col­or of a flame – Na⁺ turns flame yel­low.

Re­ac­tion of sodi­um with oxy­gen

When sodi­um burns in oxy­gen, the main prod­uct of re­ac­tion will not be sodi­um ox­ide, but sodi­um per­ox­ide:

2Na + O₂ = Na₂O₂ (sodi­um ox­ide Na₂O also forms in this re­ac­tion, but in trace quan­ti­ties).

In air, sodi­um can also swift­ly ox­i­dize to sodi­um ox­ide (the ox­ide will not be pure, as a con­sid­er­able (some­times greater) quan­ti­ty of per­ox­ide Na₂O₂ will be present among the prod­ucts):

4Na + O₂ = 2Na₂O.

The re­ac­tion of sodi­um with oxy­gen may be writ­ten as fol­lows:

6Na + 2O₂ = Na₂O₂ + 2Na₂O.

Re­ac­tion of sodi­um with non-met­als

Sodi­um, be­sides com­bus­tion, is ca­pa­ble of tak­ing part in many oth­er re­ac­tions with non-met­als:

• re­ac­tion with hy­dro­gen with for­ma­tion of hy­dride:

2Na + H₂ = 2NaH (re­ac­tion takes place with heat­ing to 250-400 ᵒC (482-752 ᵒF) and at in­creased pres­sure);

• re­ac­tion with sul­fur with for­ma­tion of sul­fides:

2Na + S = Na₂S (sodi­um sul­fide);

• re­ac­tion with halo­gens:

2Na + Cl₂ = 2Na­Cl (sodi­um chlo­ride);

2Na + Br₂ = 2NaBr (sodi­um bro­mide);

Metal­lic sodi­um re­acts poor­ly with ni­tro­gen (the re­ac­tion may be con­duct­ed in a glow dis­charge – a burn­ing dis­charge formed in a low cur­rent and with low gas pres­sure):

6Na + N₂ = 2Na₃N.

Re­ac­tion of sodi­um with met­als

When the sur­face of metal­lic sodi­um con­tacts mer­cury, an amal­gam is formed – an al­loy of met­al with mer­cury.

With potas­si­um, the met­al forms an al­loy with the for­mu­la NaK. It is quite ag­gres­sive – it may com­bust in air. If the con­tent of potas­si­um in the al­loy varies from 40% to 90% in re­la­tion to sodi­um, the al­loy re­mains liq­uid at room tem­per­a­ture. The sodi­um-potas­si­um al­loy NaK is ob­tained by al­loy­ing liq­uid potas­si­um hy­drox­ide KOH with melt­ed metal­lic sodi­um. This re­ac­tion is car­ried out at a tem­per­a­ture of 400-450 ᵒC (752-842 ᵒF).

Re­ac­tion of sodi­um with com­pounds

Sodi­um re­acts with wa­ter

Ow­ing to its chem­i­cal re­ac­tiv­i­ty, sodi­um may en­ter into re­ac­tions with var­i­ous com­pounds, for ex­am­ple:

• re­ac­tion of sodi­um with acids (di­lut­ed):

2Na + 2HCl = 2Na­Cl + H₂ (sodi­um chlo­ride NaCl and hy­dro­gen gas H₂ form).

• re­ac­tion with ni­tric and sul­fu­ric acids:

8Na + 8H₂­SO₄ = NaHS + 7NaH­SO₄ + 4H₂O (with heat­ing, con­cen­trat­ed acid);

8Na + 10H­NO₃ = 8NaNO₃ + NH₄NO₃ + 3H₂O (di­lut­ed acid – 3-5%);

11Na + 14H­NO₃ = 11­NaNO₃ + NO + N₂O + 7H₂O (acid of 20% con­cen­tra­tion).

• re­ac­tion with wa­ter (re­ac­tion takes place vig­or­ous­ly):

2Na + H₂O = 2NaOH + H₂.

• re­ac­tion with sodi­um per­ox­ide:

2Na + Na₂O₂ = 2Na₂O.

With am­mo­nia 2 types of re­ac­tion are pos­si­ble:

• re­ac­tion of sodi­um with am­mo­ni­um gas:

2Na + 2NH₃ = 2NaN­H₂ + H₂ (sodi­um amide forms with heat­ing to 350 ᵒC, or 662 ᵒF);

• dis­solv­ing sodi­um in liq­uid am­mo­ni­um:

Na + 4NH₃ = Na[NH₃]₄ (re­ac­tion with for­ma­tion of tetra sodi­um amide takes place in cold – cool­ing to -40 ᵒC (also -40 ᵒF)).

Here you’ll find an in­ter­est­ing ex­per­i­ment with am­mo­nia so­lu­tion.

Re­ac­tions of sodi­um with or­gan­ic ma­te­ri­als

Sodi­um has also found an ap­pli­ca­tion in or­gan­ic chem­istry – it is used to ob­tain al­co­ho­lates from al­co­hols:

2C₂H₅OH + 2Na = 2C₂H₅ONa + H₂ (from ab­so­lute (wa­ter­less) ethanol, sodi­um ethy­late C₂H₅ONa forms).

Sodi­um is also used to ex­tend car­bo­hy­drate chains in the Wurtz re­ac­tion:

CH₃-CH₂-Br + Br-CH₂-CH₃ + 2Na = CH₃-CH₂-CH₂-CH₃ + 2NaBr.

Sodi­um breaks bromine atoms off mol­e­cules of bromine ethyl. The “con­nec­tion” of formed car­bo­hy­drate rad­i­cals takes place with for­ma­tion of a longer mol­e­cule – the two ethyl rad­i­cals CH₃-CH₂- con­nect, form­ing the n-bu­tane mol­e­cule CH₃-CH₂-CH₂-CH₃).

Sodi­um is of­ten used as a re­duc­er in met­al­lur­gy and a dry­ing agent of or­gan­ic sol­vents (for ex­am­ple es­ters) in or­gan­ic syn­the­sis. The met­al is also used for the man­u­fac­ture of high-ca­pac­i­ty bat­ter­ies.