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Discrete Molecules

Edexcel AS-level ChemistryTopic 4 of 2125 lessons

Revision notes for Discrete Molecules in Edexcel Chemistry (8CH0). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.

  1. Simple MoleculesNon-metals can exist as molecules formed from covalently bonded atoms or in the case of carbon and silicon giant covalent lattices.
  2. Expanded Octet RuleThe octet rule and expanded octet rule determine how many valence electrons there are.
  3. Displayed FormulaeA displayed formula shows all the bonds in the molecule as individual lines.
  4. Dative Covalent BondsA dative covalent bond is formed when an empty orbital of one atom overlaps with an orbital containing a non-bonding pair (lone pair) of electrons…
  5. Electron Pair Repulsion TheoryThe Electron Pair Repulsion Theory states that electron pairs arrange themselves around a central atom so that the repulsion between them is a…
  6. The Shapes of MoleculesElectron pairs arrange themselves around a central atom so that the repulsion between them is a minimum.
  7. Molecules with Multiple BondsDouble Bonds with two bonding pairs (linear): oxygen O=O carbon dioxide O=C=O carbon disulfide S=C=S Triple Bonds with three bonding pairs (linear)…
  8. Bond AnglesThe bond angles depend on the number of bonding areas and the number of lone pairs.
  9. Shape and PolarityThe drift of bonded electrons towards the more electronegative element results in a dipole.
  10. Polyatomic IonsThe carbonate CO32- and nitrate ions NO3- are trigonal planar as they both have three bonding regions of electron density surrounding the central…
  11. London ForcesAt any one instant there is an uneven distribution of electrons.
  12. Permanent DipolesIf molecules have a permanent dipole the molecules will interact if aligned correctly.
  13. Hydrogen BondsHydrogen bonding occurs when hydrogen is bonded to a very small, highly electronegative atom (nitrogen, oxygen or fluorine).
  14. Intermolecular Forces and Boiling PointsFor simple molecules boiling temperatures are determined by the strength of the intermolecular force.
  15. Anomalous Properties of WaterHydrogen bonding in water causes it to have anomalous properties such as high melting and boiling points, high surface tension and a higher density…
  16. SolventsNon-polar substances mostly dissolve in non-polar solvents and ionic or polar substances dissolve in polar solvents such as water.
  17. Dissolving Ionic SolidsWhen a solid dissolves the ionic lattice breaks down or dissociates (endothermic) and the ions become hydrated (exothermic).
  18. Metallic LatticesAll metals are solid at room temperature with the exception of mercury.
  19. Giant Ionic LatticesIons attract oppositely charged ions in all directions resulting in a giant ionic lattice.
  20. Giant Covalent LatticesMost non-metals exist as simple covalent molecules.
  21. DiamondIn diamond, each carbon atom forms four sigma bonds to 4 other carbon atoms in a tetrahedral arrangement with all bond angles 109.5°.
  22. GraphiteIn graphite, each carbon atom forms three sigma bonds to 3 other carbon atoms forming interlocking hexagonal rings with bond angles 120°.
  23. GrapheneGraphene is a single layer of graphite.
  24. Molecular LatticesIodine and ice exist as molecular lattices.
  25. Structure and Bonding QuestionExam questions often ask you to explain a property, usually a melting point or electrical conductivity, in terms of structure and bonding.

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