Thursday 4 August 2011

Chemistry: properties of oxides from Li to Cl

To access the document version of this chapter of notes click the "Notes Corner" above.

(You can refer to wikipedia for the structures of some oxdies, especially 1) oxides of nitrogen, 2) oxides of chloride.)

Reaction of period 3 elements with water
1) 2Na + 2H2O 2NaOH + H2
2) Mg(s) + H2O(g) (note: steam is used) MgO + H2
3) Cl2 + H2O HCl + HOCl (hypochlorous acid)
Other gives no reaction with water. Al forms oxide to prevent reactions with water.
Oxides of period 2, 3 elements
-          Most element forms one type of oxides only with oxoanion O2-.
-          C forms CO and CO2; N forms N2O, NO, N2O3, NO2, N2O4, N2O5; P forms P4O6 and P4O10 (in excess oxygen); S form SO2 and SO3, Cl forms Cl2O, ClO2, Cl2O6 and Cl2O7.

-          Since F is more electronegative than O, we write F2O rather than OF2. The electronegativity of Cl and O is similar so the order can be OCl or ClO.
-          Na forms peroxide (O22-) as Na2O2 besides Na2O.
-          Oxygen won't form oxide, but it exists in forms of oxygen O2 or ozone O3.
Bonding and acidity
-          Li, Na, Mg forms ionic bonds to give oxides. These oxides are basic, dissolving in water to give alkali. E.g. Na2O + H2O 2NaOH and MgO + H2O Mg(OH)2 (slightly soluble only)
-          Peroxide reacts with water to give hydroxide ion: O22- + 2H2O 2OH- + H2O2
-          Be and Al forms ionic bonds with covalent character to gives oxides. Note that these two oxides are giant covalent structures. Their oxides are amphoteric (both acidic and basic, but NOT neutral) because they neutralize with acid and form complex with alkali.
Al2O3 + 6H+ 2Al3+ + 3H2O    Al2O3 + 2OH- + 3H2O 2[Al(OH)4]- (aluminate ion)
BeO + 2H+ Be2+ + H2O    BeO + 2OH- + H2O [Be(OH)4]2- (beryllate ion)
-          The rest forms covalent bonds to gives acidic oxides. They dissolve in water to give aqueous acid.
B2O3 + 3H2O 2H3BO3 (Boric acid)       CO2 + H2O H2CO3 (carbonic acid)
2NO2 + H2O HNO3 (nitric(V) acid) + HNO2 (nitric(III) acid) (N2O4 gives the same reaction)
N2O5 + H2O 2HNO3                              OF2 + H2O 2HF + O2
SiO2 is weakly acidic and has no reaction with water but with boiling strong alkali by the following equation: SiO2 + 2NaOH Na2SiO3 + H2O (That's why burette shouldn't be treated with NaOH.)
P4O6 + 6H2O 4H3PO3 (phosphorous acid)
P4O10 + 2H2O 4HPO3 (metaphosphoric acid, vigorously in cold water)
P4O10 + 6H2O 4H3PO4 (phosphoric acid in warm water)
SO2 + H2O H2SO3 (Sulphuric(IV) acid)     SO3 + H2O H2SO4 (Sulphuric(VI) acid)
Cl2O + H2O 2HOCl (Chloric(I) acid)       Cl2O7 + H2O 2HClO4 (Chloric(VII) acid)

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