Period 3
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Explain why sodium is more reactive than magnesium.
→ Na has a lower nuclear charge → weaker attraction between nucleus & outer electron → ∴ outer e- is lost more easily than in Mg
Describe the reaction between sodium and cold water. Give the equation.
→ reacts vigorously, forms a ball + fizzes 2Na + 2H₂O → 2NaOH + H₂
Describe the reaction between magnesium and cold water. Give the equation.
→ reacts slowly, forms weak alkaline solution Mg + 2H₂O → Mg(OH)₂ + H₂
Describe the reaction between magnesium and steam. Give the equation.
→ fast reaction Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
Explain why the reaction between magnesium and water produces a weak alkaline solution.
→ Mg(OH)₂ is produced which is sparingly soluble → ∴ low concentration of OH- in solution
State the formulas of the compounds formed when period 3 elements react with oxygen.
→ Na₂O → MgO → Al₂O₃ → SiO₂ → P₄O₁₀ → SO₂
How is SO₃ made?
→ reaction between sulfur & oxygen → at high temperature → with a catalyst
Explain why MgO has a higher melting point than Na₂O.
→ MgO lattice consists of 2+ ions which are more strongly attracted to oxygen ions → stronger ionic bonding ∴ more energy required
Explain why Al₂O₃ has a lower melting point than MgO.
• Al³⁺ ions distort oxygen’s electron cloud • this means there is some covalent character • ∴ less energy required to break the bonds
Explain why silicon dioxide has a high melting point (compared to other non-metal oxides).
→ macromolecular structure → with many strong covalent bonds → requires high amounts of energy to breaks
Explain why P₄O₁₀ and SO₂ have low melting points.
→ simple molecular structures → so weak intermolecular forces (VDW) → less energy required
How do period 3 oxides react with water?
ionic oxides → form hydroxides non-metal oxides → form acids
Give the equation for the reaction between sodium oxide and water. State the pH of the solution formed.
Na₂O + H₂O → 2NaOH pH 13
Give the equation for the reaction between magnesium oxide and water. State the pH of the solution formed.
MgO + H₂O → Mg(OH)₂ pH 9
Give the equation for the reaction between phosphurus oxide and water. State the pH of the solution formed.
P₄O₁₀ + 6H₂O → 4H₃PO₄ pH 0
Give the equation for the reaction between sulfur dioxide and water. State the pH of the solution formed.
SO₂ + H₂O → H₂SO₃ pH 3
Give the equation for the reaction between sulfur trioxide and water. State the pH of the solution formed.
SO₃ + H₂O → H₂SO₄ pH 0
State why silicon dioxide and aluminium oxide do not react with water.
insoluble in water due to their structures
Explain what is meant by the term amphoteric.
acts as both a base and an acid
State which period 3 oxide is classified as amphoteric.
aluminium oxide
Reaction between magnesium oxide and hydrochloric acid.
MgO + 2HCl → MgCl₂+ H₂O
Reaction between sodium oxide and hydrochloric acid.
Na₂O + 2HCl → 2NaCl + H₂O
Reaction between sodium oxide and sulfuric acid.
Na₂O + H₂SO₄ → Na₂SO₄ + H₂O
Reaction between phosphurus oxide and sodium hydroxide.
P₄O₁₀ + 12NaOH → 4Na₃PO₄ + 6H₂O