Period 3: Trends, Properties and their Oxides

why is Na+ more reactive Mg+ ?

amount of energy required to remove one electron from Na is less than energy required to remove 2 from Mg

Na + cold H2O

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g) vigorously fizzes with water

Mg + cold H2O

Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g) sparingly soluble, reacts slowly with water

Mg + steam

Mg(s) + H2O(g) → MgO(s) + H2(g) bright white flame

Na + O2

2Na(s) + 1/2O2(g) → Na₂O(s) bright yellow flame

m.p. metal oxides

• Na2O has high mp because of giant ionic lattice

• MgO has higher because it has a higher charger density

• Al2O3 distorts the electron cloud - it has some covalent character, less energy required to break the bonds

m.p. covalent oxides

• SiO macromolecular structure strong covalent bonds, high mp

• P₄O₁₀ & SO2 are simple covalent weak IMFs

P burned in O2

P₄(s) + 5O₂(g) → P₄O₁₀(s)

S burned in O2

S(s) + O2(g) → SO2(g)

with catalyst & high temp. 2S(s) + 3O2(g) → 2SO3(g)

how can you distinguish between SO2 and SO3?

universal indicator

SO2 → orange-red

SO3 → red

P4O10 + base

P₄O₁₀ (aq) + 12NaOH (aq) → 4Na₃PO₄ (aq) + 6H2O (l)

SO2 + base

2NaOH(aq) + SO2 (aq) → Na2SO3 (aq) + H2O (l)

SO3 + base

2NaOH (aq) + SO3 (g) → Na₂SO4 (aq) + H2O (l)

Al + base

2NaOH (aq) + Al2O3 (s) + 3H2O (l) → 2NaAl(OH)4 (aq)

Al + acid

3H2SO4 (aq) + Al2O3 (s) → Al2(SO4)3 + 3H2O(l)