Principles of Chemical Reactions

  1. Atoms combine in fixed proportions to form chemical compounds.
  2. The symbols for the atoms in a compound are combined with the numbers of atoms (as a subscript) in that compound to give a chemical formula. Examples: NaCl, H2O, CO2
  3. Atoms with filled outer shells are in a stable condition.
  4. A filled shell often has 8 electrons (an octet), this stable condition is called the Rule of Eight.
  5. The substances that undergo a chemical reaction are called the reactants. The substances created by the chemical reaction are the products .
  6. The total mass of reactants must equal the total mass of products. This is called the Law of Conservation of Mass.
  7. The rate of chemical reactions, how fast they proceed, is increased by:
    • increasing the temperature.
    • increasing the concentration of reactants.
    • increasing the surface area of reactants.
    • adding a catalyst.
  8. Atoms can transfer e- (ionic bond) or share e- (covalent bond) to achieve a filled outer shell.
  9. The outer shell is also called the valence shell and the e- are called the valence electrons.
  10. A Lewis diagram is used to show just the outer shell electrons. The electrons are shown as dots surrounding the element chemical symbol. Below are the Lewis diagram representations for hydrogen, sodium, nitrogen, oxygen and chlorine.
    lewis diagrams