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• Age of Earth: 4.5 billion years
• There was no life 4 billion years ago
• Atmosphere


  Made of water vapour & gases
• Was CO2 prevalent (common) in the primitive atmosphere? If not, why? Refer to Theme 2
• Bombardment


  The primitive atmosphere was continuously bombarded by UV, volcanic heat, radioactive decay & lightning

  
• The reactions led to the formation of first carbon-based molecules (origin of life, Theme 2)
• First cells (protobionts) were eventually formed from the carbon-based (organic) molecules created under the condition of the primitive Earth
• Life as we know it, is dependent on carbon-based (made up of carbon atoms) molecules
• Abiogenesis hypothesis


  The hypothesis that was tested in the Miller's experiment
• Miller's experiment


  1. Reactants

  2. Significance of methane

  3. Reactant that can substitute methane

  4. Products

  5. Source of energy

  6. Type of reaction

  7. Use of closed apparatus

  8. Conclusion
• Cells are 70–95% water, the rest consists mostly of carbon-based compounds
• Carbon


  Unparalleled in its ability to form large, complex, and diverse molecules

  
• Molecules that distinguish living matter from non-living matter


  • Proteins
  • Nucleic acids
  • Carbohydrates
  • Lipids
  • Other carbon-based molecules
• Carbon-based compounds/molecules


  Organic compounds/molecules = Macromolecules
• Differences between inorganic and organic molecules


  • Inorganic molecules usually contain positive & negative ions
  • Inorganic molecules usually have ionic bonding
  • Inorganic molecules are usually associated with non-living matter
  • Organic molecules always contain carbon & hydrogen
  • Organic molecules always have covalent bonding
  • Organic molecules may be quite large with many atoms
  • Organic molecules are usually associated with living organisms
• Inorganic molecules


  • C2H2NO
  • H3PO2
  • H2SO4
  • CaCl2
  • H2O
• Organic molecules


  • C2H4
  • C2H4O2
• Organic compounds are not found only in living things
• Electron configuration


  Indicates the kinds & number of bonds an atom will form

  
• Ways to illustrate electron configuration


  • Orbital diagram
  • Electron configuration notation
• Carbon has 4 valence electrons (tetravalent) – it can form 4 covalent bonds

  
• Carbon and silicon


  Belong to the same group, expected to have the same chemical properties
• Reasons why the evolution of organic molecules favoured carbon and not silicon


  • Carbon forms strong covalent bonds
  • Carbon can form double and triple bonds, and ring structures

  
• Covalent bonds


  Relatively strong bonds compared to ionic bonds or Van der Waals forces
• Carbon symbols (Cs) have been omitted in some of the structures
• The two similarities between the 5 structures are that they all have branching points and they all have different shapes and lengths
• Molecular formula


  Consists of the chemical symbols for the constituent elements followed by numeric subscripts indicating the actual numbers of each type of atom per molecule
• Structural formula


  Shows the types, numbers and arrangement of atoms in a molecule

  
• Empirical formula


  Gives the simplest whole number ratio of atoms of each element present in a compound
• Hydrocarbons


  Organic molecules consisting of only carbon & hydrogen
• Hydrocarbons are considered to be less diverse because they exist as linear (unbranched), branched & ring structures

  
• Non-polar molecules (hydrocarbons)


  Not attracted to water (hydrophobic)
• Many organic molecules, such as fats, have hydrocarbon components. That is, hydrocarbons are not found in living things as individual (separate) molecules, but bonded (attached) to other polar molecules. Living things evolved that arrangement

  
• Hydrocarbons can undergo reactions that release a large amount of energy
• Isomers


  Compounds with the same molecular formula but different structures and properties
• Types of isomers


  • Structural isomers
  • Stereoisomers (geometric isomers and optical isomers)
• The similarity between glucose and D-Glyceraldehyde is that they are both stereoisomers

  
• The similarity between Figure 1 and 2 is that they are both structural isomers
• The isomers illustrated in Figure 1 are structural isomers because they have different covalent arrangements (orders) of their atoms

  
• Geometric isomers (stereoisomers)


  Have the same covalent arrangements but differ in spatial arrangements