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Topic 4 (Strand 11: VSEPR theory (Molecules with non-bonding domains…

- - - - Note: Oxygen and Nitrogen have a double and a triple bond.
- - - - Polar covalent bonds occur between atoms that have a difference in electronegativity of between 0.5 and 1.7 units. In these molecules, the bonding electrons are not equally shared between the atoms. The polarity of the H-X bond decreases as you descend the group.
    - - Non-polar covalent bonds occur between atoms that have a small difference in electronegativity, of between 0.0 and 0.4 units. In these molecules, the bonding electrons are equally shared.
      - Examples are any molecule that is composed of the same element. O2, H2 etc.
- - - - Atoms in molecules that are electron deficient are able to form coordinate covalent bonds. An example of a molecule that has coordinate covalent bonds is aluminium chloride. At high temperatures, aluminium chloride exists as molecules with the formula AlCl3. This molecule is electron deficient; it still needs two electrons to complete the octet in the outer shell of the aluminium atom. At lower temperatures, two molecules of AlCl3 combine to form a dimer with the formula Al2Cl6. The AlCl3 molecules are able to combine because lone pairs of electrons on two of the chlorine atoms form coordinate covalent bonds with the aluminium atoms