(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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