METAL OXIDES

• WHAT ARE THE METAL OXIDES OF PERIOD 3 LIKE?

  • Na2O, MgO, Al2O3
  • giant ionic lattices
  • high melting points
  • but Al2O3 has some covalent character (Al forms very small ion with large positive charge, so electron cloud is distorted)
  • larger difference in electronegativities leads to a greater ionic character
• WHAT ARE THE NON-METAL OXIDES OF PERIOD 3 LIKE?

  • SiO2 is giant covalent
  • has high melting point as strong covalent bonds must be broken
  • P4O10, SO2, SO3 exist as simple covalent molecules
  • have weak van der Waals and dipole-dipole forces
  • have relatively low melting points that increase along the period
  • P4O10 are solids
  • SO2/ SO3 are gases at 298K
• OXO-ACIDS?

  • phosphoric (V) acid, sulfuric (VI) acid, sulfuric (IV) acid
  • anions formed
  • bonding electrons spread equally across all bonds
  • perfect tetrahedron
  • due to delocalisation
  • except in sulfuric (IV) acid, in which the bond angle decreases to 106 degrees due to lone pair
• FORMULA OF OXO-ACIDS?

  Phosphoric acid: H3PO4

  Sulfuric (IV) acid: H2SO3

  Sulfuric (VI) acid: H2SO4