Chemical properties of group16, Chemistry

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+ Na2Sn

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  (M2-).

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

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