Q. Chemical Properties of group16?

Oxygen is slightly less reactive than the halogens but reacts directly with nearly all the elements except the noble gases, the halogens and a few noble metals. Despite the high bond dissociation energy of 0₂(498 kJ mol^-1), these reactions are frequently highly exothermic and, once initiated, can continue spontaneously or even explosively. For example, its reactions with carbon and hydrogen producing CO₂, and Hz O₂, respectively.

C(s) + O₂ (g) ------------> CO₂ (g) DH= 394 kj mol^-1

2H2 (g) + O₂ (g) -----------> 2H₂O (l) DH= -568 kj mol ^-1

Sulphur is also a very reactive element, particularly at slightly high temperatures. It reacts slowly with Hz at 390 K, more rapidly above 473 K. Hot concentrated HNO, oxidises S to H₂S0₄.

S+ 6HNO₃--------------> H₂SO₄+ 6NO₂+ 2H₂O

Sulphur dissolves in hot alkali giving a mixture of sulphide and sulphite as the first products. These react with excess of S giving polysulphides of the type Na2S, and some thiosulphate, Na₂S₂0,

3S+ 6NaOH --------------> 2Na₂S+ Na₂SO₃+ 3H₂O

Na₂S+ Na₂So₃+ Ns---------> Na₂S₂O₃+ Na₂S_n

It reacts with halogens to give compounds like SF₆ SF₄,  S₂Cl₂,  S₂Br₂, etc. The non-metals react with sulphur mostly at elevated temperatures. Sulphur compounds exhibit humerous possible oxidation states, from -2 to +6. You will study about them in the next section.

Selenium, tellurium and polonium combine directly with most elements, though less readily than do 0 and S, the most stable compounds are the selenides, tellurides and polonides  (M^2-).

They form compounds with electronegative elements 0, F and CI in which the oxidation states are +2, +4 and +6.a