periodicity

• Periodicity

  A repeating trend in properties of the elements across each period of the periodic table.
• Proton number

  The number of protons in the nucleus of an atom, also known as atomic number.
• Group

  A vertical column in the periodic table. Elements in a group have similar chemical properties and their atoms have the same number of outer shell electrons
• across period 2 and 3

  • melting point increases from Group 1 to Group 14 (4)
  • there is a sharp decrease in melting point between Group 14 (4) and Group 15 (5)
  • the melting points are comparatively low from Group 15 (5) to Group 18 (0)
• Giant metallic structures in period 2:

  • Li
  • Be
• Giant metallic structures in period 3:

  • Na
  • Mg
  • Al
• Giant covalent structures in period 2:

  • B
  • C
• Giant covalent structure in period 3:

  • Si
• N2, O2, F2 and Ne are simple molecular structures
• P4, S8, Cl2 and Ar are simple molecular structures
• Across Period 2 and Period 3, the trend in meting point relates to the structure of the elements

  • The melting point increases from Group 1 to Group 14 because the elements have giant structures (metallic and then covalent)
  • The melting points decrease from group 14 to 15 because the structure changes to simple molecular, which is only held together by weak intermolecular forces
• Across the period, the atomic radius decreases as effective

  nuclear charge increases and there is no increase in shielding