properties of period 3 elements and their oxides (A2 inorganic chemistry) Flashcards
how does sodium react with water?
reacts vigorously with cold water forming a ball and fizzing
produces hydrogen gas and an alkaline solution of sodium hydroxide
2Na (s) +2H₂O (l) -> 2NaOH (aq) + H₂ (g)
how does magnesium react with water?
reacts slowly with cold water forming a weak alkaline solution of magnesium hydroxide
this is a weak alkaline solution as magnesium hydroxide is sparingly soluble so there are little OH⁻ ions in solution
Mg (s) + 2H₂O (l) -> Mg(OH)₂ (aq) + H₂ (g)
however, magnesium reacts much faster with steam to form magnesium oxide
Mg (s) + 2H₂O (g) -> MgO (s) + H₂ (g)
explain the trends in the reactions of the period 3 elements with oxygen
period 3 elements react to form oxides
sulfur is an exception, it forms sulfur dioxide, and can form SO₃ with a catalyst and higher temperatures
sodium oxide: 2Na (s) + 1/2O₂ (g) -> 2Na₂O (s)
magnesium oxide: Mg (s) + 1/2O₂ (g) -> MgO (s)
aluminium oxide: 2Al (s) + 1/2O₂ (g) -> Al₂O₃ (s)
silicon dioxide: Si (s) + O₂ (g) -> SiO₂ (s)
phosphorous(V) oxide: P₄ (s) + 5O₂ (g) -> P₄O₁₀ (s)
sulfur dioxide: S (s) + O₂ (g) -> SO₂ (g)
S (s) + O₂ (g) -> 2SO₂ (g) + 2O₂ -> 2SO₃ (g)
how do the period 3 elements react with air?
sodium: very fast, forms Na₂O
magnesium: very fast, forms MgO
aluminium: slow, but fast if powdered, forms Al₂O₃
silicon: slow, forms SiO₂
phosphorous: spontaneously combusts, forms P₄O₁₀
sulfur: steadily burns, forms SO₂
explain the trend in melting point of period 3 oxides
Na₂O, MgO, and Al₂O₃ all have high melting points as they form giant ionic lattices with a lot of strong attractive forces which require lots of energy to overcome
MgO has a higher melting point than Na₂O as magnesium forms +2 ions which are attracted more strongly to the oxygens
Al₂O₃ has a lower meting point than MgO as the Al³⁺ ions have a higher charge density and polarising power that pull oxygen towards itself which distorts the electron cloud of oxygen and give the bond some covalent character which make less energy required to break the bonds
SiO₂ has a higher melting point than the rest of the non-metal oxides as it forms a giant covalent structure with many strong covalent bonds that require a not of every to overcome
P₄O₁₀ and SO₂ have lower melting points as they form simple molecular structures with weaker intermolecular forces that don’t require as much energy to break
give the reactions of the ionic oxides formed when period 3 metals react with water
ionic oxides form alkaline solutions when added to water, as they contain the O²⁻ ion which accepts protons from the water molecules when dissolved in solution to form OH⁻ ions
sodium oxide: dissolves readily to form an alkaline solution of pH 12-14
Na₂O (s) + H₂O (l) -> 2NaOH (aq)
magnesium oxide: sparingly soluble so will dissolve less strongly and form an alkaline solution of pH 9-10 as there are less OH⁻ ions in solution
MgO (s) + H₂O (l) -> Mg(OH)₂ (aq)
give the reactions of the simple covalent oxides formed when period 3 elements react with water
simple covalent oxides form acids when added to water to form solutions of pH 0-2 (assuming a minimum concentration of 1moldm⁻³)
the acids dissociate in solution forming H⁺ ions and conjugate bases (negative ions)
phosphoric(V) acid: P₄O₁₀ (s) + 6H₂O (l) -> 4H₃PO₄ (aq)
H₃PO₄ (aq) -> 3H⁺ (aq) + PO₄²⁻ (aq)
sulfuric(IV)/sulfurous acid: SO₂ (g) + H₂O (l) -> H₂SO₃ (aq)
H₂SO₃ (aq) -> 2H⁺ + SO₃²⁻ (aq)
sulfuric(VI) acid: SO₃ (l) + H₂O (l) -> H₂SO₄ (aq)
H₂SO₄ (aq) -> 2H⁺ + SO₄²⁻ (aq)
give the reactions of the silicon and aluminium oxides formed when period 3 elements react with water
silicon dioxide forms macromolecular structure with many strong covalent bonds, therefore it is insoluble in water
however it is classed as an acid as it will react with a base to form a salt
aluminium oxide has both covalent and ionic character and is insoluble in water
it will react with both acids and bases to form salts so it amphoteric
give the reactions of period 3 basic oxides with acids and bases
magnesium oxide: 2HCl (aq) + MgO (s) -> MgCl₂ (aq) + H₂O (l)
sodium oxide: H₂SO₄ (aq) + Na₂O (s) -> Na₂SO₄ (aq) + H₂O (l)
give the reactions of period 3 acidic oxides with acids and bases
silicon oxide: 2NaOH (aq) + SiO₂ (s) -> Na₂SiO₃ (aq) + H₂O (l)
phosphorous pentoxide: 12NaOH (aq) + P₄O₁₀ (s) -> 4Na₃PO₄ (aq) + 6H₂O (l) <- always produces a phosphate (PO₄)
sulfur dioxide: 2NaOH (aq) + SO₂ (g) -> Na₂SO₃ (aq) + H₂O (l) <- sodium sulfite produced
sulfur trioxide: 2NaOH (aq) + SO₃ (g) -> Na₂SO₄ (aq) + H₂O (l) <- sodium sulfate produced
give the reactions of period 3 amphoteric oxides with acids and bases
aluminium oxide as an acid: 2NaOH (aq) + Al₂O₃ (s) + 3H₂O (l) -> 2NaAl(OH)₄ (aq)
aluminium oxide as a base: 3H₂SO₄ (aq) + Al₂O₃ (s) -> Al₂(SO₄)₃ (aq) + 3H₂O (l)
when aluminium oxide acts as an acid, only a salt is produced and water is on the reactants side
