Lesson 1: Homologous Series

A homologous series is a family of compounds that differs only by the length of its hydrocarbon chain. (Ex: Alkanes - CH₄, C₂H₆, C₃H₈)

Members share:

• General formula

• Chemical properties

As you go down a homologous series, chain gets longer, the boiling point increases: Gas → Liquid → Solid.

Types of Formulas

Empirical formula - smallest whole number ratio.

Molecular formula - actual number.

Full structural formula - displayed formula. Drawn structure and arrangement of atoms.

Condensed Structural Formula - Similar to molecular formula but in order of bonds.

Lesson 2: Isomers (and naming)

Compounds with the same molecular formula but different structural formulas. (Same number of each atom, but bonded in a different order).

Naming

Lesson 3: Meet the Families

Alkanes

Alkanes really don’t do much.

• Combustion is one of two notable reactions, hence, we use them for fuels.

Complete combustion:

• Alkane + O₂ → CO₂ + H₂O

Incomplete combustion:

• Alkane + O₂ → C + CO + CO₂ + H₂O

Alkanes are stable because they have full valence shells and high bond enthalpies.

Halogenation

Alkanes will undergo halogenation if reacted with a halide in the presence of U.V. light.

C₂H₆ (g) + Cl₂ (g) → CH₃CH₂Cl (g) + HCl (g)

Radicals

Radicals are species with unpaired electrons.

Halogens form radicals when hit by U.V. light of the right frequency.

Cl₂ → 2Cl*

The asterisk represents the unpaired electron.

This process is called homolytic fission - the bond breaks equally with one electron going to each chlorine.

Free Radical Substitution

Cl₂ + uv → 2Cl*

Initiation - radicals formed by homolytic fission.

Cl* + C₂H₆ → C₂H₅ + HCl

C₂H₅* + Cl2 → C₂H₅Cl + Cl*

Propagation - these steps feed each other the radicals needed to continue.

Cl* + Cl* → Cl₂

Cl* + C₂H₅* → C₂H₅Cl

C₂H₅* + C₂H₅* → C₄H₁₀ Termination - any two radicals can combine to terminate the reaction.

Crude Oil

We get residual fuel oil, lubricating oils, diesel, kerosene, naphtha, gasoline blending components, and refinery gases from crude oil.

Lesson 4: Molecular Modelling

Lewis Structure

1. Count valence electrons.

2. Determine central atom.

   • Most unpaired electrons.

   • Least electronegative.

3. Add surrounding with bonding pair - subtract electrons from total.

4. Subtract octets from total.

5. Make multiple bonds to complete octets.

VSEPR

Group of negative charge will repel one another - negatively charged centers / electron domains.

Lesson 5: Alkenes

Alkenes are considerably more reactive that alkanes and are a major industrial feedstock.

The reactivity is due to the double bond:

• The double bond contains 4 electrons.

• This is a significant amount of charge which:

  • Makes it attractive to electrophiles.

  • Enables it to polarise approaching molecules.

Most reactions of alkenes are addition reactions. All reactions remove the double bond.

Alkenes and hydrogen

Alkene + hydrogen (H₂) → alkane

Reaction conditions:

• Hot >120°

• Ni catalyst

Alkenes and hydrogen halides

Alkene + hydrogen halide (H-Br) → halogenoalkane

Reaction conditions:

• This reaction occurs very readily and needs no special conditions.

Alkenes and halogens

Alkene + halogen (Cl-Cl) → dihalogenoalkane

Reaction conditions:

• This reaction occurs very readily and needs no special conditions.

Standard test for alkenes:

• Halogen used in aqueous solution of bromine becomes decolourised.

Polymerisation

Alkene + alkene → Polymer

Reaction conditions:

• Vary from alkene to alkene but often include high pressure, temperature, and a catalyst.

Alkenes and water

Alkene + water (H₂O) → alcohol

Reaction conditions:

• Water must be steam.

• Phosphoric or sulphuric acid catalyst.