Nitrogen and oxygen and their interaction

We consider nitrogen inert. But is it?

[Deposit Photos]

This ar­ti­cle will dis­cuss oxy­gen and ni­tro­gen – two gas­es that read­i­ly re­act with each oth­er.


It's hard to pin­point the first sci­en­tist to ob­tain ni­tro­gen, but Hen­ry Cavendish was cer­tain­ly among them. In his lab­o­ra­to­ry in 1772, Cavendish used a spe­cial de­vice to pass air over heat­ed coals. Af­ter re­peat­ing this process sev­er­al times, he then treat­ed the air with al­ka­lis. Cavendish called the sub­stance ob­tained in the ex­per­i­ment a “suf­fo­cat­ing” gas be­cause of its prop­er­ties. But the sci­en­tist couldn’t un­der­stand just what the suf­fo­cat­ing gas was. Armed with mod­ern chem­istry knowl­edge, how­ev­er, we can rea­son that pass­ing air over heat­ed coals binds car­bon diox­ide, and that the al­ka­li neu­tral­izes it. The re­main­ing "suf­fo­cat­ing" part of the air con­sists, for the most part, of mol­e­cules of N₂.Cavendish re­port­ed his find­ings to his col­league, Joseph Priest­ley.

In­trigu­ing­ly, this is not the first case when sci­en­tists did not un­der­stand the sub­stance that they had cre­at­ed in their ex­per­i­ments. For ex­am­ple, Priest­ley once bond­ed oxy­gen and ni­tro­gen us­ing elec­tric cur­rent, but did not un­der­stand that he had ob­tained ar­gon, an in­ert gas.

Phys­i­cal prop­er­ties of ni­tro­gen

In stan­dard con­di­tions, ni­tro­gen is an in­ert, col­or­less gas with no smell or taste. It is harm­less to hu­man be­ings, and is lighter than air, but isn’t as light as he­li­um or hy­dro­gen. The gas is also vir­tu­al­ly in­sol­u­ble in wa­ter and does not re­act with it.

The sev­enth el­e­ment in the pe­ri­od­ic ta­ble can also ex­ist in liq­uid and sol­id ag­gre­gate states.

Liquid nitrogen [Deposit Photos]

In a liq­uid state, ni­tro­gen boils at -195.8 °C, where­as in a sol­id state it melts at -209.86 °C.

Chem­i­cal prop­er­ties

Ni­tro­gen mol­e­cules are quite sta­ble; they are di­atom­ic and form a triple bond. Thus, the mol­e­cules prac­ti­cal­ly nev­er break apart, and the sev­enth el­e­ment demon­strates low chem­i­cal ac­tiv­i­ty. Con­verse­ly, ni­tro­gen com­pounds are high­ly un­sta­ble – heat­ing them forms free ni­tro­gen.

Re­ac­tions with met­als

Molec­u­lar ni­tro­gen can only en­ter into a re­ac­tion with a small group of met­als, all of which dis­play re­duc­ing prop­er­ties. For ex­am­ple, N₂ can re­act with lithi­um:

6Li + N₂ = 2Li₃N

It also re­acts with the light-sil­very met­al mag­ne­sium, but only at tem­per­a­tures above 300 °C. This re­ac­tion yields mag­ne­sium ni­tride – yel­low-green crys­tals which, when heat­ed, break down into mag­ne­sium and free ni­tro­gen:

3Mg + N₂ = Mg₃N₂.

Mg₃N₂ → 3Мg + N₂↑— at a tem­per­a­ture of 1000 °C or high­er.

If the ni­tride of an ac­tive met­al is added to wa­ter, the process of hy­drol­y­sis be­gins, yield­ing the hy­drox­ide of the met­al and am­mo­ni­um.

Ni­tro­gen and hy­dro­gen

Ni­tro­gen and hy­dro­gen re­act at a tem­per­a­ture of around 400 °C, with a pres­sure of 200 at­mos­pheres and in the pres­ence of por­ous iron act­ing as a cat­a­lyst:

3H₂ + N₂ = 2NH₃.

[Deposit Photos]

Re­ac­tion of ni­tro­gen and oth­er non-met­als

All in­ter­ac­tions of sub­stances with ni­tro­gen take place at high tem­per­a­tures. Take, for ex­am­ple, boron:

2B + N₂ = 2BN

It does not in­ter­act with many halo­gens, or with sul­fur, but sul­fides and halo­genides may be ob­tained in­di­rect­ly.

Re­ac­tion of ni­tro­gen with oxy­gen

Oxy­gen is an el­e­ment with the atom­ic num­ber 8. It is a trans­par­ent gas with no smell or col­or, and is blue in its liq­uid form.

Liquid oxygen [Wikimedia]

Oxy­gen can also ex­ist in a sol­id ag­gre­gate state of blue crys­tals. It has di­atom­ic mol­e­cules.

In­ter­est­ing­ly, Priest­ley did not ini­tial­ly un­der­stand that he had dis­cov­ered oxy­gen, and be­lieved that he had ob­tained a cer­tain com­po­nent of air. Priest­ley ob­served the break­down of mer­cury ox­ide in a her­met­ic de­vice. The sci­en­tist used a lens to di­rect rays of sun­light to the ox­ide.

As for the in­ter­ac­tion of ni­tro­gen and oxy­gen, the sub­stances re­act in the pres­ence of an elec­tric cur­rent, be­cause ni­tro­gen is a sta­ble mol­e­cule and re­acts un­will­ing­ly with oth­er sub­stances:

O₂ + N₂ = 2NO

There are sev­er­al ox­ides of ni­tro­gen, the ox­i­da­tion state of which varies from one to five.

Sev­er­al com­pounds can form from a re­ac­tion be­tween ni­tro­gen and oxy­gen:

  • N₂O — ni­trous ox­ide;

  • NO — ni­tric ox­ide;

  • N₂O₃ — dini­tro­gen tri­ox­ide;

  • NO₂ — ni­tro­gen diox­ide;

  • N₂O₅ — ni­tro­gen pen­tox­ide.

Click here for an in­ter­est­ing ex­per­i­ment that in­volves ob­tain­ing ni­tro­gen diox­ide and study­ing its prop­er­ties.

Ni­trous ox­ide, an anes­thet­ic, is ob­tained via the break­down of am­mo­ni­um ni­trate. It is a col­or­less gas with a char­ac­ter­is­tic pleas­ant smell. The ox­ide dis­solves well in wa­ter.

Molecule of nitrous oxide [Wikimedia]

N₂O is also a con­stant com­po­nent of air. The process takes place at a tem­per­a­ture of 200 °C. The re­ac­tion is:

NH₄NO₃ = 2Н₂О + N₂O↑

Ni­tric ox­ide, NO, is also a col­or­less gas that is al­most in­sol­u­ble in wa­ter. This com­pound does not read­i­ly re­lease oxy­gen, but it is known for its ad­di­tion re­ac­tions, such as with tox­ic, green-yel­low chlo­rine gas:

2NO + Сl₂ = 2N­O­Cl.