FREE JAMB LECTURE NOTES

March 6, 2010

ATOMIC STRUCTURE

  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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