IB DP Chemistry: SL复习笔记4.3.5 Trends in Melting Points of Metals

• The strength of electrostatic attraction can be increased by:
  • Increasing the number of delocalised electrons per metal atom
  • Increasing the positive charges on the metal centres in the lattice
  • Decreasing the size of the metal ions
• These factors can be seen in the trends across a period and down a group

Melting points of metals across a period

• If you compare the electron configuration of sodium, magnesium and aluminium you can see the number of valence electrons increases
  • Na = 1s²2s²2p⁶3s¹
  • Mg = 1s²2s²2p⁶3s²
  • Al  = 1s²2s²2p⁶3s²3p¹ 
• Aluminium ions are also a smaller size than magnesium ions or sodium ions and these two factors lead to stronger metallic bonding which can be seen in the melting points
• The stronger the metallic bonding, the more energy is need to break the metallic lattice and so the higher the melting point
• As we go across period 3 we can see the effect of stronger metallic bonding on the metals
  • Remember only the first three elements have metallic bonding in this graph

Melting points as you go across a period. The metallic bonding gets stronger from Na to Al

Melting points of metals down a group

• As you go down the group the size of the cation increases so this decreases the attraction between the valence electrons and the metallic lattice, leading to a reduction of the melting point

Melting points as you go down a group of metals. The metallic bonding gets weaker from Li to Cs