Period 3

• Which Period 3 element has a simple atomic structure?

  Argon
• Period 3 elements like sodium exhibit metallic bonding.
• Van der Waals forces are present between atoms in argon.
• What is the trend in atomic radius across Period 3?

  Decreases
• The first ionization energy across Period 3 generally increases due to increasing nuclear charge.
• Aluminium and sulfur are exceptions to the ionization energy trend in Period 3.
• What happens to electronegativity across Period 3?

  Increases
• When sodium reacts with water, it melts into a ball and dissolves exothermically.
• What is the balanced equation for the reaction of sodium with water?

  Na(s) + H₂O (1) NaOH(aq) + H₂(g)
• Magnesium hydroxide formed from the reaction of magnesium with cold water is highly soluble.

  False
• What is formed when magnesium reacts with steam?

  MgO
• Aluminium does not react with water due to its oxide coating.
• Silicon, phosphorus, and sulfur do not react with water.
• What is the balanced equation for the reaction of chlorine with water?

  Cl₂ + H₂O HCl + HCIO
• The reaction of chlorine with water is an example of disproportionation.
• Argon reacts with water.

  False
• What is the balanced equation for the reaction of sodium with oxygen?

  2Na + ½O₂ → Na₂O
• Metal oxides in Period 3 are basic compounds.
• Silicon dioxide is formed from the reaction of silicon with oxygen.
• What type of flame is produced when sulfur reacts with oxygen?

  Blue
• Non-metal oxides in Period 3 are acidic compounds.
• Sulfur dioxide can react with oxygen to form sulfur trioxide.
• Which Period 3 oxide has the highest melting point?

  MgO
• Ionic metal oxides have high melting points due to strong electrostatic attractions.
• Why does silicon dioxide have a higher melting point than phosphorus(V) oxide?

  Strong covalent bonds
• Metal oxides of Period 3 react with water to form solutions containing hydroxide ions.
• Aluminium oxide is insoluble in water.
• What is the key property of aluminium oxide that allows it to react with both acids and bases?

  Amphoteric
• The covalent oxides of Period 3 are generally acidic.
• Amphoteric substances can act as both acids and bases.
• What is formed when aluminium oxide reacts with sodium hydroxide?

  NaAl(OH)₄
• When aluminium salts dissolve in water, they form acidic solutions due to the formation of the hexaaqua ion [Al(H₂O)₆]³⁺.
• Adding a strong base to an aqueous solution of [Al(H₂O)₆]³⁺ forms a white precipitate of aluminium hydroxide.
• What is the balanced equation for the reaction of [Al(H₂O)₆]³⁺ with hydroxide ions?

  [Al(H₂O)₆]³⁺(aq) + 3OH⁻(aq) → Al(H₂O)₃(OH)₃(s) + 3H₂O(l)
• Aluminium hydroxide is amphoteric because it reacts with both acids and bases.