Chemical Reactions - Introduction Notes

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 total mass of substances that undergo a chemical reaction (reactants) in a chemical reaction must equal the total mass of substances created by the chemical reaction (products). This is called the Law of Conservation of Mass.
6. 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.
7. Atoms can transfer e^- (ionic bond) or share e^- (covalent bond) to achieve a filled outer shell.
8. 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.
   
9. The outer shell is also called the valence shell and the e^- are called the valence electrons.