Chemical reactions

1.2.3 Trends within the periodic table

2.1.2 Ionic compounds

Chemical reactions

  1. Compounds are substances in which atoms of two or more elements are chemically combined
  2. Chemical bonding involves atoms either transferring or sharing electrons in their highest occupied energy levels in order to attain the electron arrangement of the nearest noble gas, forming ions or molecules
  3. Chemical reactions can be represented by word equations or by symbol equations
  4. In reversible reactions, the products can react to form the original reactants and are denoted with a double harpoon: A+B ⇌ C+D
  5. Information about the states of substances in a reaction can be included in symbol equations by subscripting each substance with a state symbol: (s), (l), (g), (aq)
  6. No atoms are lost or made during a reaction so the mass of the products is equal to the mass of the reactants
  7. The masses of reactants and products can be calculated from balanced symbol equations by matching up the molar ratios and translating that into a mass

  8. Even though no atoms are lost or made in a reaction, it is not always possible to obtain the calculated amount of a product:

    1. The reaction may not go to completion because it is reversible
    2. Some of the product may be lost when it is separated from the reaction mixture
    3. Some of the reactants may react in ways different from the expected reaction