Chemistry: properties of oxides from Li to Cl

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(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 O^2-.

-          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 (O₂^2-) 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: O₂^2- + 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)