Comprehensive Study Guide: Organic Chemistry, Bonding, Polymers, and Earth Resources

Chemical Bonding and Molecular Structure

• Covalent Bonding:

  • Occurs when two or more non-metal atoms share electrons to achieve a stable outer electron shell configuration.
  • All hydrocarbons are formed through covalent bonding.
  • Properties of Covalent Molecular Compounds:
  • Exist as gases, liquids, or solids with low melting and boiling points due to weak intermolecular forces of attraction between molecules.
  • Do not conduct electricity because they are composed of neutral molecules rather than free ions or delocalised electrons.
  • Are generally insoluble in water.

• Valency and Chemical Formulas:

  • Valency is defined as the number of electrons an atom must gain, lose, or share to obtain a full outer shell, achieving a stable noble gas configuration.
  • Carbon Disulfide ($CS_2$):
  • Carbon (atomic number $6$) has an electron configuration of $2,4$.
  • Sulfur (atomic number $16$) has an electron configuration of $2,8,6$ (has $6$ valence electrons and a valency of $2$).
  • Valency balance equation: $1 \times 4 = 2 \times 2$
  • Formula and bonding: Chemical formula is $CS_2$ ($1$ molecule). Each sulfur atom needs to gain $2$ electrons, and carbon needs to share $4$ electrons.
  • Lewis dot diagram: $:\ddot{S}::C::\ddot{S}:$
  • Structural diagram: $S=C=S$ (contains double covalent bonds).
  • Phosphorus Trichloride ($PCl_3$):
  • Phosphorus (atomic number $15$) has an electron configuration of $2,8,5$ and a valency of $3$
  • Chlorine (atomic number $17$) has an electron configuration of $2,8,7$ and a valency of $1$
  • Valency balance equation: $3 \times 1 = 1 \times 3$
  • Chemical formula: $PCl_3$
  • Lewis dot diagram: Central phosphorus atom sharing single electron pairs with three surrounding chlorine atoms.
  • Structural diagram: Central $P$ single-bonded to three $Cl$ atoms.
  • Chlorine Gas ($Cl_2$):
  • Each chlorine atom shares one electron to gain a full outer shell.
  • A straight line represents a shared pair of two electrons, called a single covalent bond.
  • 

• Metallic Bonding:

  • Metal atoms have valence electrons that are held loosely.
  • Valence electrons become delocalised, forming a mobile "sea" of delocalised electrons flowing throughout the structure.
  • When valence electrons delocalise, metal atoms become positively charged ions (cations).
  • The positive metal ions arrange into a closely packed metallic lattice.
  • There is a strong electrostatic attraction between positive metal ions and the surrounding sea of delocalised electrons acting in all directions, holding the lattice together.
  • The overall charge of the metallic lattice remains neutral.
  • Properties of Metals:
  • High melting and boiling points.
  • Mostly solid at room temperature.
  • Malleable (can be hammered or bent into shape).
  • Ductile (can be drawn into thin wires).
  • Lustrous (shiny appearance).
  • Good thermal and electrical conductors due to freely moving delocalised electrons.

Organic Chemistry and Hydrocarbons

• Organic vs. Inorganic Compounds:

  • Organic Compounds: Molecules composed of carbon and hydrogen atoms, often accompanied by elements such as oxygen, nitrogen, and fluorine. Examples include methane ($CH_4$), keratin, and DNA. Carbon forms a wide variety of compounds because it possesses $4$ valence electrons.
  • Inorganic Compounds: Molecules primarily held together by ionic bonding.

• Hydrocarbons:

  • Covalently bonded molecules composed entirely of carbon and hydrogen atoms.

• Fractional Distillation of Crude Oil:

  • Crude oil, natural gas, and coal are fossil fuels, which are non-renewable finite resources.
  • Fractional distillation separates hydrocarbon mixtures based on differing boiling points.
  • Procedure: The mixture is heated in a furnace and pumped into a fractionating column that is cool at the top ($<40^\circ\text{C}$) and very hot at the bottom ($>600^\circ\text{C}$). Vapours rise, condensing and evaporating repeatedly, allowing fractions with similar boiling points to be collected at specific levels.
  • 
  • Hydrocarbon Fractions (ordered from top to bottom of the column):
  • Petroleum / Refinery Gases: Boiling point $<40^\circ\text{C}$. Includes methane, ethane, propane, and butane. Used as general fuels; propane and butane are stored in gas bottles for cars, stoves, caravans, and barbecues.
  • Petrol / Gasoline: Boiling point $40-205^\circ\text{C}$. Contains hydrocarbons with $5$ to $10$ carbon atoms per molecule ($C_5-C_{10}$). Used as motor vehicle fuel and for manufacturing plastics and detergents.
  • Naphtha: Boiling point $60-100^\circ\text{C}$. Contains hydrocarbons with $8$ to $12$ carbon atoms per molecule ($C_8-C_{12}$). Used in motor vehicle fuel, plastics, pesticides, fertilisers, and rubber processing.
  • Kerosene: Boiling point $175-325^\circ\text{C}$. Contains hydrocarbons with $10$ to $16$ carbon atoms per molecule ($C_{10}-C_{16}$). Used as aviation fuel, paint solvents, and paraffin for heating and lighting.
  • Diesel Oils: Boiling point $250-350^\circ\text{C}$. Contains hydrocarbons with $14$ to $20$ carbon atoms per molecule ($C_{14}-C_{20}$). Used as fuel for trucks, trains, cars, domestic heaters, and asphalt production.
  • Heavy Crude Oils / Lubricating Oils: Boiling point $300-370^\circ\text{C}$. Contains hydrocarbons with more than $20$ carbon atoms per molecule ($C_{>20}$). Processed into lubricating oils, petroleum jelly, candle wax, and bitumen.
  • Fuel Oil: Boiling point $370-600^\circ\text{C}$. Used for ships and heating.
  • Residue: Boiling point $>600^\circ\text{C}$. Bitumen used for road surfaces.

IUPAC Nomenclature and Hydrocarbon Reactions

• IUPAC Naming Systems for Hydrocarbons:

  • Alkanes (suffix -ane): Saturated hydrocarbons containing single-bonded carbon atoms ($C-C$). Saturated indicates that all atoms are held together by single bonds. They are fairly unreactive but burn efficiently.
  • Alkenes (suffix -ene): Unsaturated hydrocarbons containing double-bonded carbon atoms ($C=C$).
  • Alkynes (suffix -yne): Unsaturated hydrocarbons containing triple-bonded carbon atoms ($C\equiv C$).

• Straight-Chain Alkane Series ($C_1$ to $C_{10}$):

  • Methane: $CH_4$
  • Ethane: $C_2H_6$
  • Propane: $C_3H_8$
  • Butane: $C_4H_{10}$
  • Pentane: $C_5H_{12}$
  • Hexane: $C_6H_{14}$
  • Heptane: $C_7H_{16}$
  • Octane: $C_8H_{18}$
  • Nonane: $C_9H_{20}$
  • Decane: $C_{10}H_{22}$

• Combustion Reactions:

  • Definition: A chemical reaction where a fuel reacts rapidly with oxygen, releasing energy in the form of heat and light along with water vapour.
  • Complete Combustion:
  • Occurs when a fuel burns in a plentiful supply of oxygen.
  • Exothermic reaction involving complete oxidation, producing carbon dioxide ($CO_2$) and water ($H_2O$).
  • Releases all stored chemical energy, producing a hot blue flame.
  • Word Equation: Fuel + Oxygen $\rightarrow$ Carbon Dioxide + Water + Energy
  • Chemical Equation: $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O + \text{Energy}$
  • Incomplete Combustion:
  • Occurs when oxygen supply is restricted or limited.
  • Exothermic reaction that produces water ($H_2O$), toxic carbon monoxide gas ($CO$), and solid carbon soot ($C$).
  • Glow Mechanism: Fuel cannot burn completely, forming unburnt carbon soot particles. Heat causes these particles to glow yellow and orange (incandescence), masking blue light.
  • Word Equation: Fuel + Oxygen (limited) $\rightarrow$ Water + Carbon / Carbon Monoxide + Energy
  • Chemical Equations:
    • Moderate oxygen limitation: $2CH_4 + 3O_2 \rightarrow 2CO + 4H_2O + \text{Energy}$
    • Severe oxygen limitation: $CH_4 + O_2 \rightarrow C + 2H_2O + \text{Energy}$

Polymer Science and Synthetics

• Polymer Definitions:

  • Polymer: A long macromolecule composed of repeating monomer units linked by covalent bonds.
  • Monomer: Small reactive molecules, mostly containing carbon, but can also contain hydrogen, oxygen, chlorine, fluorine, and nitrogen.
  • Natural Polymers: DNA, wool, natural rubber, cellulose, proteins, starch.
  • Synthetic Polymers: Plastics, nylon, polyester, polystyrene.
  • Petrochemicals: Chemicals derived from crude oil and natural gas used as raw materials for synthetic polymers.

• Industrial Production of Polymers:

  1. Crude oil is extracted from underground deposits and transported to oil refineries.
  2. Crude oil is separated into fractions by boiling point via fractional distillation (Naphtha is the key fraction for plastic manufacture).
  3. Cracking: Long-chain hydrocarbons are broken down into smaller alkenes (monomers like ethene, propene, butene).
  4. Polymerisation: Monomer molecules chemically link together into polymer chains (e.g., ethene $\rightarrow$ polyethylene; propene $\rightarrow$ polypropene).
  5. Polycondensation: Monomers join to form a polymer chain while releasing a small byproduct molecule such as water ($H_2O$), alcohol, or ammonia ($NH_3$).
  • 

• Structural Classes of Polymers:

  • Thermoplastic Polymers:
  • Consist of long polymer chains held together by weak intermolecular bonds.
  • Soften when heated and can be repeatedly melted, reshaped, and recycled.
  • Mechanism: Heating breaks weak intermolecular bonds, allowing chains to slide past one another. Upon cooling, weak bonds re-form, hardening the polymer.
  • Examples: Polyethylene, Polyvinyl chloride (PVC), Nylon.
  • 
  • Thermosetting Polymers:
  • Consist of polymer chains bound by strong covalent cross-link bonds in a rigid 3D network.
  • Hard, rigid, and highly heat-resistant.
  • Mechanism: Strong heating breaks covalent cross-links, causing chemical decomposition and charring instead of melting. Cannot be remoulded or recycled.
  • Examples: Bakelite, Melamine.
  • 
  • Elastomers:
  • Natural or synthetic rubber-like polymers with light cross-linking.
  • Highly elastic, flexible, and capable of shock absorption. Can be thermoplastic or thermosetting.
  • 

• Resin Identification Codes (The 7 Types of Plastics):

  • 
  • 1. PET / PETE (Polyethylene Terephthalate):
  • Properties: Waterproof, heat-resistant, tough, insoluble.
  • Uses: Soda bottles, water bottles, food packaging.
  • Recyclable: Yes.
  • 2. HDPE (High-Density Polyethylene):
  • Properties: Waterproof, semi-flexible, solid, heat-resistant.
  • Uses: Milk jugs, detergent bottles, shampoo containers.
  • Recyclable: Yes.
  • 3. PVC (Polyvinyl Chloride):
  • Properties: Transparent or translucent, tough, solid, long-term stability.
  • Uses: Pipes, window frames, vinyl flooring, medical equipment.
  • Recyclable: Rarely.
  • 4. LDPE (Low-Density Polyethylene):
  • Properties: Tough, flexible, sometimes sticky surface, heat-resistant.
  • Uses: Plastic bags, six-pack rings, food containers, plastic wraps.
  • Recyclable: Yes, but uncommon.
  • 5. PP (Polypropylene):
  • Properties: Excellent chemical resistance, tough but flexible.
  • Uses: Food containers, bottle caps, straws, textiles, automotive parts.
  • Recyclable: Yes.
  • 6. PS (Polystyrene):
  • Properties: Glass-like surface, hard, vulnerable to solvents.
  • Uses: Disposable coffee cups, plastic food boxes, cutlery, insulation.
  • Recyclable: Rarely.
  • 7. OTHER / Other:
  • Properties: Diverse mixed polymers, difficult to recycle, often contains harmful properties.
  • Uses: Sunglasses, compact discs, baby bottles, large water jugs.
  • Recyclable: Rarely.

Earth Resources and Mineral Processing

• Resource Classifications:

  • Natural Resource: Any material derived from nature (e.g., water, air, sunlight, forests, soil, animals, fossil fuels, metals).
  • Renewable Resource: Resources capable of naturally replenishing within a human lifetime.
  • Non-Renewable / Finite Resource: Natural materials existing in fixed amounts that cannot be replaced on a human timescale once consumed (e.g., coal, natural gas, crude oil, metal ores).

• Common Metal Ores and Constituent Elements:

  • 
  • Aluminium: Ores = Bauxite, Alumina; Other elements = Gallium, Oxygen.
  • Titanium: Ores = Rutile, Ilmenite; Other elements = Oxygen.
  • Lead: Ore = Galena; Other elements = Sulfur.
  • Lithium: Ore = Spodumene; Other elements = Oxygen, Aluminium, Silicon.
  • Iron: Ores = Magnetite, Hematite; Other elements = Oxygen.
  • Uranium: Ore = Uraninite (Pitchblende); Other elements = Oxygen.
  • Copper: Ore = Chalcopyrite; Other elements = Sulfur, Iron.
  • Zinc: Ore = Sphalerite; Other elements = Sulfur.

• Commercial Uses of Extracted Metals:

  • 
  • Iron (from Hematite): Steel production for structural building, general construction, appliances, cans, engine blocks.
  • Aluminium (from Bauxite): Electrical equipment, automotive parts, aircraft, ships, cans, aluminium foil, cooking utensils.
  • Copper (from Chalcopyrite): Electrical wiring, water and gas piping, light fixtures, heat exchangers in air conditioners/refrigerators/car radiators, plumbing fittings, alloys.
  • Zinc (from Sphalerite): Galvanising iron and steel to prevent rusting, alloy manufacturing.
  • Lead (from Galena): Storage batteries (car batteries), radiation shields, scuba weights, solder, ammunition.

• Mining Terminology and Production Stages:

  • 
  • Overburden:
  • Production Stage: Pre-mining / Extraction.
  • Definition: The top layer of soil, rock, and ecosystem sitting directly above a mineral deposit. Must be physically removed before chemical extraction.
  • Examples: Soil, gravel, and bedrock covering a coal seam.
  • Gangue:
  • Production Stage: Mining / Ore Processing.
  • Definition: Commercially worthless rock, sand, or minerals physically mixed in with valuable ore. Mined with the ore and separated mechanically.
  • Examples: Quartz, calcite, or sandstone embedded alongside gold or copper.
  • Slag:
  • Production Stage: Smelting / Refining.
  • Definition: Glass-like non-metallic byproduct formed during chemical smelting. Created when leftover gangue melts and reacts with an added purifying flux.
  • Examples: Calcium silicate ($CaSiO_3$), which floats to the top of molten iron and is skimmed off.

• Metal Extraction Stages:

  1. Mineral Extraction: Physical separation of ore from unwanted gangue (crushing, grinding, sieving, washing).
  2. Metal Extraction: Chemical separation breaking chemical bonds (e.g., Smelting using heat and reducing agents; Electrolysis passing an electrical current through molten ore).
  3. Metal Purification: Refining processes removing final chemical impurities to obtain pure metal.

• Environmental Impacts and Land Rehabilitation:

  • Benefits of Mining: Provides structural raw materials, creates jobs, generates export revenue, supplies energy sources, provides minerals for green technologies.
  • Environmental Disadvantages:
  • Habitat destruction, land degradation, loss of biodiversity.
  • Sulfur dioxide ($SO_2$) emissions react with moisture to form sulfurous and sulfuric acid ($H_2SO_4$), causing acid rain that damages ecosystems and infrastructure.
  • Tailings dams store solid metal waste; leaching occurs when rainwater dissolves toxic chemicals, contaminating soil and groundwater.
  • Subsidence: Sinking of surface land into hollow mine voids.
  • Carbon emissions contributing to climate change.
  • Rehabilitation Procedures:
  • Native seed collection and nursery propagation prior to clearing.
  • Overburden is used to backfill open-cut mine holes.
  • Topsoil is reapplied over overburden to restore essential growth nutrients.
  • Soil contours are shaped to integrate naturally with surrounding landforms.
  • Environmental Impact Statement (EIS):
  • Document prepared prior to project approval to assess potential ecological effects.
  • Details strategies to minimise damage to local ecosystems, ground water, air quality, and outlines waste management and site rehabilitation plans.