March 8, 2010

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March 6, 2010


Filed under: CHEMISTRY REVIEW NOTES — Tarebi @ 10:52 pm
  1. Postulates
    • Particles of matter are in a constant state of motion
    • These particles posses kinetic energy because of the constant motion
    • The temperature of a body/substance depend on the kinetic energy of its particles
    • Particles in solids, liquids and gases have different degree of motion
  1. Particles in solid state
    • Closely and firmly packed and held together by strong forces of cohesion
    • Only vibrate and rotate
    • Have definite shape, volume
    • Difficult to compress
  2. Particles in liquid state
    • Not closely packed as in solid state due to weaker forces of attraction
    • Can vibrate, rotate and translocate (i.e move from one place to another)
    • Fixed volume but no definite shape( assumes the shape of their container)
    • Difficult to compress
  3. Particles in gaseous state
    1. Have very high kinetic energy (i.e free to move about)
    2. Cohesive forces are negligible
    3. Have no definite shape ( occupy the shape of their container)
    4. Easily compressed
  1. Change in temperature
    • Main factor for change in the state
    • Particles gain more kinectic energy when heat is applied
    • The following processes can be explained by the kinetic theory of matter
    • Melting
    • Boiling
    • Freezing
    • Evaporation
  2. Melting
    • When heat is applied to a solid, its particles gain more kinetic energy and thus vibrate and rotate  more violently
    • A point is reached when the forces of vibration overcome the forces of cohesion
    • At this point or temperature (called the melting point) the crytalline structure of the solid suddenly breaks down
    • At the melting point a solid changes either into a liquid ( liquification) or gas(sublimation)
    • Note that the presence of an impurity decreases the melting point of the solid
  3. Evaporation
    • At a given temperature, some of the particles in a liquid have more kinetic energy than the others
    • These particles escape from the liquid into the air when  they get to the surface of the liquid
    • This process is called evaporation
    • If evaporation occurs in a closed container, the evaporated particles accumulate above the liquid and exact a pressure called vapour pressure. Some of the vapour particles collide with the liquid surface, loose their kinetic energy and re-enter the liquid. This is called condensation.
    • At equillibrium ( i.e when evaporation equals condensation) the vapour pressure becomes constant. This is called saturated vapour pressure of the liquid
    • The temperature of the liquid decreases if evaporation continues.
  4. Boiling
    • Like in melting, when heat is applied to a liquid, its particles gain kinetic energy and move more freely. Thus increasing the rate of evaporation
    • As the rate of evaporation increases, the saturated vapour pressure also increases
    • The liquid boils at a temperature when the saturated vapour pressure equals the atmospheric pressure
    • The temperature at which boiling ocurs is called the boiling point
    • Note that a rise in atmospheric pressure will increase the boiling point while a fall in atmospheric pressure will decrease the boiling point
    • Presence of impurities in the liquid will also increase the boiling point


  1. Dalton’s atomic theory
    1. Main postulates
      1. Elements are made up of atoms
      2. Atoms can neither be created nor destroyed
      3. Atoms of the same element are alike
      4. Atoms combine in simple ratio
      5. Chemical reactions are due to combination or separation of atoms
  2. Atomic structure
    1. Particles of atoms
      1. Proton wit positive charge
      2. Electron with negative charge
      3. Neutron with no charge
    2. Location
      1. Proton and neutron are in the nucleus
      2. Electrons revolve round the nuleus in shells or orbits
      3. Electron shells:  K, L, M, N, O, P
    3. Atomic number and atomic mass
      1. The number of protons in the nucleus of an atom is the atomic number Z
      2. Mass number A is the sum total of the protons and neutrons in the nuleus of an atom.
      3. The difference between A and Z gives the number of neutrons
    4. Electronic configuration
      1. Shows how electrons are distributed in different shells ( K, L, M, N, O, P)
      2. Electonic shells have suborbits
        1. s-orbit ( spherical in shape), max electrons 2
        2. p-orbit ( shape of dumb-bell), max electrons 6
        3. d-orbit, max electrons 10
        4. f-orbit
      3. The rare gases are chemically stable because they have an octet structure.

Table 3.1 electronic shells and their sub-orbits

Electronic shell Suborbit Max number of electrons
K or 1 S 3
L or 2 S, p 8
M or 3 S, p, d 18
N or 4 f *
  1. Chemical combinations/bonds
    1. Two major types
      1. Electronic or ionic
      2. Covalent
        1. Simple covalent
        2. Coordinate covalent
    2. Electrovalent combination
      1. Transfer of electrons from a donor atom to an acceptor atom
      2. Metals are usually donors, non-metals are acceptors
      3. Donors with one valence electron ( Na, K) are most reactive, acceptors with seven valence electrons  (Cl )are most reactive.
      4. Donors become positively charged while acceptors negatively charged after  the electron transfer.
      5. A strong electrostatic force binds the ions together to form the ionic bond
      6. Electrovalent compounds (NaCl, MgO, MgCl2, CaCO3)
        1. Solid structure
        2. High boiling and melting point
        3. Electrolytes
        4. Dissolve in polar solvent ( ethanol, water)
    3. Ordinary covalent combination/bond
      1. No transfer of electrons
      2. A pair of electrons  is shared between the two reacting atoms
      3. Covalent bond exists between the atoms ( single, double, triple)
      4. Common in molecules of diatomic elements e.g O2, H2
      5. Covalent compounds ( N2, C2H2, CO2, CH4, H2O, NH3)
        1. Gases or volatile liquids
        2. Low melting and boiling point
        3. Non-electrolytes
        4. Dissolve in non-polar solvents ( benzene)
    4. Coordinate covalent combination
      1. A lone pair of electrons is donated for sharing by one of the  reacting atoms.
      2. Example of compounds with  coordinate covalent bond
        1. Ammonium ion
        2. Oxonium ion
    5. Chemical bonding forces
      1. Electrovalent bond
      2. Covalent bond
      3. Metallic bond
      4. Hydrogen bond
      5. Van der Waals forces

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