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 equation, observations, pH

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

pH = 13

Mg + cold H2O equation, observations and pH

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

pH = 9

Mg + steam equation and observations

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

Na + O2 equation and observations

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

Mg burned equation and observations

Mg + O2 → MgO white flame and white solid

Al + O2 (burned) equations and observations

4Al + 3O2 → 2Al2O3

white flame + white powder

Si + O2 equations and observationsx

Si + O2 → SiO2 white flame and white solid formed

P burned in O2 equations & observations

P₄(s) + 5O₂(g) → P₄O₁₀(s) white flame and white solid formed

S burned in O2 equation and observations

S(s) + O2(g) → SO2(g)

blue flame choking acidic gas

S + O2 burned with catalyst & high temp

2S(s) + 3O2(g) → 2SO3(g)

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

• SiO₂ macromolecular structure strong covalent bonds, high mp

• P₄O₁₀ & SO2 are simple covalent weak IMFs

how can you distinguish between SO2 and SO3?

universal indicator

SO2 → orange-red

SO3 → red

P4O10 + NaOH

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

SO2 + NaOH

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

SO3 + NaOH

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

Al₂O₃ + NaOH

role of Al₂O₃

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

aluminium oxide as an acid

Al2O3 + HCl

role of Al2O3

Al2O3(s) + 6HCl (aq) → 2AlCl3 (aq) + 3H2O (l)

aluminium oxide as a base

Al2O3 + H2SO4

role of Al2O3

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

base

P₄O₁₀ + Na₂O

P₄O₁₀ + 6Na₂O → 4Na₃PO₄

SO2 + water equation and pH

SO₂(g) + H₂O(l) → H₂SO₃ (aq) pH = 3

SO3 + water and pH

SO₃ (g) + H₂O → H₂SO₄ (aq) pH = 0

P4O10 + water and pH

P4O10 + 6H2O → 4H3PO4 pH = 0

violent exothermic reaction

why do Al2O3 and SiO2 not dissolve in water?

• Al2O3 - due to strong ionic lattice

• SiO₂ strong macromolecular structure both give pH 7

display formula of H₂SO₃

display formula of H3PO4

draw the display formula of SO2 with any lone pairs

draw the display formula of SO3

periodicity

repeating patterns of physical or chemical properties going across a period

what is the trend in atomic radius for period 3?

atomic radii decrease going across due to the increased no. of protons → more positive attraction to electrons with similar shielding

what is the trend in ionisation energy across period 3? what are the deviations

• general increase in first IE due to increasing no. of protons with similar shielding

• drop Mg → Al electron in 3p subshell, easier to remove because electrons are higher in energy

• drop P → S outer electron is paired in same orbital, slight repulsion makes it easier to remove

melting point trends Na, Mg, Al, Si

strong metallic bonding increases due to increasing charge density

Si is macromolecular - strong covalent bonds high mp

melting point trends Cl₂, S₈, P₄, Ar

simple molecular, weak van der waals

S₈ has higher mp than P₄ because there are more electrons in its van der waals

SiO2 + very concentrated NaOH

SiO₂ (s) + 2NaOH(l) → Na₂SiO₃ (aq) + H₂O(l)

MgO + phosphoric acid

3MgO + 2H₃PO₄ → Mg₃(PO4)₂ + 3H2O

how can you prove that metal oxides contain ions?

melt the solids and show that they conduct electricity

how is aluminium metal is protected from corrosion in moist air?

a thin layer of Al2O3 forms impermeable to water and air

why is Mg(OH)2 better than NaOH for treating excess acid in rivers and the stomach

sparingly soluble and weakly alkaline so using an excess would not make the water too alkaline

Na2O and water

Na₂O + H₂O → 2NaOH pH = 13