3.2.1 - Periodicity

• What is periodicity? The repeating pattern of physical/chemical properties going across the periods
• Atomic radius decreases from left to right across a period.
• What does the block of an element tell you? The subshell in which the highest energy electron is in
• How are elements in the periodic table arranged? Elements are arranged according to their proton number
• What is a period on the periodic table? The horizontal rows
• What is a group on the periodic table? The vertical columns.
• What does the group number indicate on the periodic table? The number of outer electrons of an element.
• What are the 4 blocks of the periodic table?

  • s block
  • p block
  • d block
  • f block

  
• What elements are in each block of the periodic table?

  • s-block = groups 1 and 2
  • p-block = groups 3 to 0
  • d-block = transition metals
  • f-block = radioactive elements
• Along a period, atomic radius decreases.
• Going down a group, atomic radius increases.
• Along a period, ionisation energy increases
• Ionisation energy increases along a period

  
  

  Because:

  • atomic radius decreases, hence nuclear charge increases.
  • This means that the outer electrons are held more strongly so more energy is required to remove the outer electron and ionise the atom.
• Going down a group, ionisation energy decreases
• Ionisation energy decreases going down a group because:

  • The nuclear attraction between the nucleus and outer electrons reduces and shielding also increases.
  • Both of these factors mean less energy is required to remove the outer electron.
• What does the melting point of Period 3 elements depend on?

  • The structure of the element
  • The bond strength
• Melting points increase across Period 3 between sodium and aluminium because

  • Sodium, magnesium and aluminium are all metals with metallic bonding.
  • Their melting points increase due to greater positive charge of their ions
• Why does the melting point increase dramatically for silicone in Period 3?

  • Silicon has a very strong covalent structure.
  • So more energy is required to break the strong covalent bonds - giving it a very high melting point
• Why does argon have an even lower melting point than chlorine ?

  • Argon is a noble gas that exists as individual atoms with a full outer shell of electrons.
  • This makes the atom very stable and the van der waals forces between them very weak.