periodicity

• Periodicity

  The regular, repeating pattern in properties (chemical and physical) of elements across periods of the periodic table
• Trend in atomic radius across elements in Period 3

  1. Atomic radius decreases

  2. Atomic number increases and so nuclear charge increases

  3. Elements have same number of electron shells - so shielding is almost constant

  4. The nucleus has a stronger attraction for the electrons
• Trend in first ionisation energy across elements in Period 3

  1. General increase

  2. Nuclear charge increases but the amount of shielding is almost constant

  3. Greater attraction between the nucleus and the outermost electrons means that more energy is required to remove an electron

  4. Exceptions are Al and S
• Groups that deviate from the general trend in Ionisation energy across a period


  • Group 3 - Aluminium: The electron being removed is from a (3)p subshell which is further away from the nucleus than the (3)s electron that is lost from Mg
  • Group 6 - Sulphur: The electron lost is from a paired (3)p orbital, the electrons repel
• Blocks on the periodic table


  • s
  • p
  • d
  • f
• Bonding type

  • Metallic
  • Macromolecular
  • Molecular
  • Atomic
• Trend in melting points across Period 3 for the elements Na‒Al

  1. Melting point increases Na to Al

  2. The charge on the metallic ion increases Na to Al

  3. The size of the metallic ion decreases

  4. The strength of the electrostatic force of attraction between the Metallic ion and the delocalised electrons increases Na to Al
• Why the melting point of Si is much higher than the other elements in Period 3

  Silicon is macromolecular with many, strong covalent bonds between Si atoms in a giant lattice
• Trend in melting/boiling point of the elements P-S-Cl in Period 3

  1. P4, S8 and Cl2 are all molecular substances with weak intermolecular forces of attraction (VdW) between molecules

  2. S8 has the highest melting point as it has the greatest Mr /most electrons

  3. Cl2 has the lowest melting point as it has the lowest Mr /least electrons

  4. Melting point S8>P4>Cl2
• Why Argon has the lowest melting and boiling point in Period 3

  Argon is monatomic with very weak Van der Waals forces of attraction between the atoms