S2.3 The Metallic Model :

S2.3.1 and S2.3.2 The Metallic Bond :

⭐️ Metallic bond is the electrostatic attraction between a lattice of cations and delocalised electrons

• Metals are found on the left side of the periodic table
• They have low ionization energies, enabling them to react with other atoms by donating their electrons and forming positive ions
• In elemental states, electrons are held loosely and are referred to as ‘delocalised’
• Metals contain a regular lattice arrangement of cations surrounded by a ‘sea’ of delocalised electrons

📌 Properties of Metals

• Physical properties
  • Lustrous – delocalised electrons in crystal structure reflect light
  • Good conductors of electricity (solid/liquid state) as electrons are free to move
  • Good conductors of heat – delocalised electrons and packed structure of ions enable efficient thermal transfer
  • Malleable and ductile – movement of delocalised electrons is non-directional so bond remains in place even under pressure
  • High melting points
• Chemical properties
  • Form cations
  • Usually form ionic compounds
  • Oxides are basic
• Non directional nature of metallic bonding allows for enhancement of properties through addition of different elements – results in the formation of alloys
• Steel is an example of an alloy of iron that contains small amounts of carbon

🔍 TOK Connect : The ability to explain natural phenomena such as metallic properties through the application of theory (eg. atomic theory) is an important feature of science.

📌 Strength of Metallic Bond

• Strength of a metallic bond depends on the charge and radius of metal ions
  • Number of delocalised electrons
  • Charge on the cation
  • Radius of the cation
• Increased delocalised electron density and smaller cations result in strong bonds (Mg has stronger metallic bonding than Na)
• Strength of metallic bonding tends to decrease down a group as the size of cations increase
• Strength of metallic bonding tends to increase across a period due to increased charge density and smaller atomic radii
• Charge density = charge/volume

S2.3.3 Transition Metals [HL]

⭐️ Transition metals are elements that have incomplete d-subshells or can give rise to cations with incomplete d-subshells

• Transition metals have high melting points
  • Close proximity in energy of 3d and 4s subshell – allows transition metals to delocalize a larger number of electrons
  • All transition metals can delocalize electrons and have small ionic radii – increases the strength of metallic bonding
  • Makes it harder to predict trends
  • Sc to V – increase in mp due to increased number of delocalised electrons
  • V – general decrease as the large amount of energy required to create +5 and +6 ions would not be paid back by the energy released by metallic bonding
• Transition metals have high electrical conductivity
  • Large number of delocalised electrons allows for easy flow of current
  • All metals can conduct electricity due to mobile electrons
  • First row transition metals (except for Copper) seem to be poorer conductors of electricity compared to metals like Aluminium,etc
  • s and p block electrons have a higher tendency to get delocalised than d block electrons – why most transition metals aren’t better electrical conductors than metals
  • Copper has an extremely high electrical conductivity and is an exception – however, its conductivity is usually explained in terms of the delocalised s electron