Period 3

• Students should be able to

  1. Explain the trend in the melting point of the oxides of the elements Na–S in terms of their structure and bonding

  2. Explain the trends in the reactions of the oxides with water in terms of the type of bonding present in each oxide

  3. Write equations for the reactions that occur between the oxides of the elements Na–S and given acids and bases
• Lewis base
• Period 3 elements in s block

  • Sodium: 1s22s22p63s1
  • Magnesium: 1s12s22p63s2
• Electronegativity increases across period 3
• Atomic radius decreases across period 3
• Amphoteric
• Bronsted-Lowry acid
• Period 3 elements in p block

  • Aluminium: 1s22s22p63s23p1
  • Silicon: 1s22s22p63s23p2
  • Phosphorus: 1s22s22p63s23p3
  • Sulfur: 1s22s22p63s23p4
  • Chlorine: 1s22s22p63s23p5
  • Argon: 1s22s22p63s23p6
• Bronsted-Lowry base
• Learning Objectives


  Demonstrating and applying knowledge and understanding of various topics related to Period 3 elements and their oxides
• Lewis acid
• First ionisation energy increases across period 3
• What determines the block that an element belongs to?
• Anomalies in the first ionisation energy trend across period 3
• Melting point trend across period 3

  Na, Mg, Al have high melting points due to strong electrostatic attraction between positive metal ions and delocalised electrons. Melting point increases across the period as metal ion size decreases and charge density increases. Si has a high melting point due to strong covalent bonds. P4, S8, Cl2 have low melting points due to weak intermolecular forces. Ar has a low melting point due to weak van der Waals forces
• Reaction of sodium with water


  Sodium metal reacts vigorously with water, producing hydrogen gas and forming a colourless solution containing sodium ions and hydroxide ions with an alkaline pH
• Decrease in 1st ionisation energy between magnesium and aluminium

  Outermost electron in a higher energy (3)p orbital in aluminium, further from the nucleus and experiencing more shielding, making it easier to remove
• Ionisation energy trend across period 3

  As you go across the period table, first ionisation energy increases due to the increase in nuclear charge, decrease in atomic radius, and constant shielding, resulting in greater attraction between the nucleus and the outer electron
• Decrease in 1st ionisation energy between phosphorus and sulfur

  Outer electrons in the 3p orbital of sulfur begin to pair up, leading to repulsion and making it easier to remove the outer electron
• Reaction of magnesium with water

  Magnesium reacts slowly with water, producing hydrogen gas and forming a solution containing magnesium ions and hydroxide ions with a slightly alkaline pH
• Reaction of silicon with oxygen

  • Si + O2 → SiO2
• Reaction of sodium with oxygen

  • 4Na + O2 → 2Na2O
• The solution that remains contains magnesium ions and hydroxide ions and has a very slightly alkaline pH (just above 7) due to the low concentration of OH- ions
• Conversion of sulfur(IV) oxide to sulfur(VI) oxide

  • 2SO2 + O2 → 2SO3
• Reaction of phosphorus with oxygen

  • P4 + 5O2 → P4O10
• A piece of magnesium ribbon will produce a small volume of hydrogen when left in contact with water for several weeks
• Reaction of magnesium with oxygen

  • 2Mg + O2 → 2MgO
• Reaction of magnesium with steam

  Mg(s) + H2O(g) → MgO(s) + H2(g)
• Reactions of the period 3 elements with oxygen


  period 3 element + oxygen → period 3 oxide
• Reaction of aluminium with oxygen

  • 4Al + 3O2 → 2Al2O3
• Reaction of sulfur with oxygen

  • S + O2 → SO2
• Conversion of sulfur dioxide to sulfur trioxide


  Reaction with more oxygen in the presence of a vanadium(v) oxide catalyst under specific conditions
• P4O10 has a higher melting point than SO3 due to a bigger Mr and stronger van der Waals intermolecular forces
• Melting point of aluminium oxide is lower than magnesium oxide due to the high charge density of the aluminium ion
• Reactions of period 3 oxides with water - Sodium oxide

  Na2O(s) + H2O(l) → 2NaOH(aq)
• Non-metal oxides structure


  • Macromolecular
• Melting points of period 3 oxides

  • Sodium oxide (Na2O), Magnesium oxide (MgO), Aluminium oxide (Al2O3)
• Non-metal oxides like silicon dioxide have high melting points due to strong covalent bonds
• Melting point of magnesium oxide is higher than sodium oxide due to the smaller ionic radius and higher charge of Mg2+ ions
• Metal oxides bonding

  • Ionic