Higher Revsion Slides

• Covalent radius


  Half the distance between the nuclei of two of its bonded atoms
• Noble gases do not have a covalent radius because they do not exist as bonded atoms
• Atomic radius


  • Increases as you go down the group due to the increasing number of electron shells, the inner electrons shield the outer electrons meaning there is less of an attraction between the nucleus and the outer electrons
• Atomic radius


  • Decreases as you go along a period due to increasing number of protons which means there is a stronger attraction between nucleus and outer electrons pulling them in closer
• Electronegativity


  A measure of an atom's attraction for bonding electrons
• Electronegativity


  • Decreases as you go down a group as there are more energy levels meaning the screening effect is greater and there is less of an attraction between the positive nucleus and the outer electrons
• Electronegativity


  • Increases as you go across a period due to the increasing number of protons. This means there is a greater attraction between the nucleus and the bonding electrons
• Ionisation energy


  The energy required to remove one mole of electrons from one mole of gaseous atoms
• Ionisation energy


  • Decreases down the groups, this is because the outer electron is further away from the positive pull of the nucleus. There will be a greater screening effect as there are more shells and the inner electrons will screen the outer electrons from the positive nucleus
• Ionisation energy


  • Increases across the period due to the increasing protons. This means there is a greater attraction between the nucleus and outer electrons
• Trends in the periodic table

  • Increasing nuclear charge across
  • Screening effect (more energy levels) down
• Bonding continuum


  • Pure covalent or non-polar there is no difference in electronegativity
  • Most covalent character
  • Most ionic character
• Exam style questions: Most ionic character = biggest difference, Least ionic character = least difference
• Exam style questions: Most covalent character = least difference, Least covalent character = most difference
• Examples of pure compounds with pure covalent bonds

  • Diatomic elements
  • Sulfur (S8)
  • Phosphorus (P4)
• Types of covalent compounds

  • Covalent molecular gases
  • Covalent network (carbon in form of graphite/diamond)
  • Covalent molecular solids (carbon in form of fullerene)
• London dispersion forces


  Electrostatic attractions between a temporary dipole and a temporary induced dipole due to the movement of electrons
• London dispersion forces


  • Very weak, resulting in low melting and boiling points
  • Bigger atom/molecule, more electrons, stronger LDF, more energy, higher mp/bp
• Substances with only London dispersion forces

  • Pure covalent molecules (diatomic elements, sulfur, phosphorus, fullerenes)
  • Noble gases
• Permanent dipole-permanent dipole forces

  Attraction between the positive dipoles of one molecule and the negative dipoles of another molecule due to the asymmetrical charge and shape
• Permanent dipole-dipole forces are stronger than London dispersion forces
• Hydrogen bonding


  A special type of dipole-dipole attraction between molecules, not a covalent bond to a hydrogen atom. It results from the attractive force between a hydrogen atom covalently bonded to a very electronegative atom such as N, O, or F atom
• Hydrogen bonding is the strongest intermolecular force but much weaker than covalent bonding
• Collision theory


  • For successful collisions the molecules need to collide with the correct orientation and energy greater than or equal to the activation energy
  • Increased temperature - more kinetic energy, move graph to the right - lower the height
  • Adding a catalyst - lower the activation energy, move activation energy line to the left
  • Increasing concentration - more molecules, start and finish at the same point but increase height of the graph
• Reaction profile


  • ΔH value is not changed when a catalyst is used, ΔH = p-r
  • Activation energy is the bottom of the hill to the top of the hill
  • The very brief stage at the point of maximum collision when some bonds are in the process of breaking while new bonds are forming is called the activated complex
• Homologous series


  • Alkanes
  • Cycloalkanes
  • Alkenes
  • Alkynes
  • Alcohols
  • Carboxylic acids
  • Esters
  • Aldehydes
  • Ketones
  • Fats and Oils
  • Amines
  • Amino acids
  • Proteins
  • Terpenes
• Be able to name and draw members of each homologous series, know their functional groups by name and be able to draw them
• Functional groups


  • Ester link
  • Peptide/Amide link
  • Amino/Amine group
• As a general rule, if the molecule contains only C and H atoms it will be non-polar, while if it also contains O or/and N atoms it is more likely to be polar. However, the non-polarity of long hydrocarbon chains/rings can cancel the effect of a single polar group and make the molecule behave as non-polar
• Ester formation


  1. Carboxylic acid + Alcohol -> Ester + Water (condensation)

  2. Water + Ester -> Carboxylic acid + Alcohol (hydrolysis)
• Ester link


  1. O from alcohol part, C=O from carboxylic acid part
• Making an ester


  Use concentrated sulfuric acid as catalyst, condenser to cool down reactants, base to neutralise excess acid, water bath as alcohols are flammable
• Esters


  • Low melting & boiling points due to weak intermolecular forces, not very soluble in water as no hydrogen bonding present
• Triglycerides


  Naturally occurring esters made up of propane-1,2,3-triol (glycerol) and 3 fatty acids
• Fats


  • Mostly saturated (C-C), can pack closer together, LDF stronger, more energy required to overcome the stronger LDF, higher melting point, solid at room temp
• Oils


  • Mostly unsaturated (C=C), loosely packed, LDF weaker, less energy required to overcome the weaker LDF, lower melting point, liquid at room temp
• Hydrogenation


  To increase the melting point of an oil, addition reactions between the double bonds and hydrogen can take place. This reduces unsaturation and causes hardening
• The bromine test can be used to determine the level of unsaturation in a fat or oil
• Proteins


  Large molecules that our cells need to function properly, consist of amino acids, the structure and function of our bodies depend on them
• Proteins contain the elements C, H, O, N