Periodicity

• Elements are classified into blocks:

  s block = groups 1 & 2

  p block = groups 3 to 0

  d block = transition metals

  f block = radioactive elements
• Atomic Radius

  Along a period atomic radius decreases due to increased nuclear charge, outer electrons are pulled in closer as increased charge produces a greater attraction.

  Down a group, atomic radius increases, increased distance between outer electrons and nucleus so reduced attraction and more shielding.
• Ionisation Energy

  Along a period, ionisation energy increases. The decreasing atomic radius and increasing nuclear charge means outer electrons are held more strongly so more energy is required to remove the outer electron and ionise the atom.

  Down the group, ionisation energy decreases. The nuclear attraction between outer electrons and nucleus and increased shielding means less energy is required to remove outer electron.
• Physical Properties of P3

  Sodium, magnesium and aluminium are metals with metallic bonding. Their melting points increase due to greater charged ions (Na = +1, Mg = +2, Al = +3).

  Silicon is macromolecular - very strong covalent structure - high melting point

  Phosphorus, sulphur, chlorine are simple (covalent) molecules held with weak van der waals forces - less energy required.

  Argon is a noble gas that exists as individual atoms with a full outer shell of electrons - making the atom stable and van der waals between them very weak so low melting point and exists as gas at room temp.
• Identify the element in P3 (from Na to Cl) that has the largest atomic radius:


  Na

  AR decreases along a period
• There is a general trend for an increase in IE across P3

  Give 1 example of an element that deviates from this trend and explain why this deviation occurs:

  Aluminium

  Its outer electron is in 3p orbital, 3p is higher in energy than 3s
• Explain why the atomic radius decreases across P3, from sodium to chlorine:

  The nuclear charge increases and shielding is similar
• State the meaning of the term periodicity:

  Repeating trends of physical properties
• Explain why the melting point of sulphur is greater than that of phosphorus:

  S8 molecules are bigger than P4 molecules

  Therefore van der waals forces between molecules are stronger in sulphur