1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s6 5f14 6d10 7p6 6f14

  1. Identify the number of electrons the element has.
  2. Fill each subshell completely until there are no more electrons needed.
  3. Do not fill a subshell if there are not enough electrons in that subshell

Oxygen -- 8 electrons

1s2 2s2 2p4 = electron configuration

Note--there are only 4 electrons in the last subshell because only 4 are needed, not a full 6.

Orbital Notation

Ions -- atoms or groups of atoms that have a positive or negative charge
  • cations -- positively charged atom or groups of atoms
  • anions -- negatively charged atom or groups of atoms

  • Chemical Formulas -- shows the kinds and numbers of atoms in a unit

  • Law of Definite Proportions -- in samples of any chemical compound, the masses of the elements are always in the same proportions

  • Law of Multiple Proportions -- whenever two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers

Rules for writing charges of ions:
  • Group 1 metals are always negative 1
  • Group 2 metals are always negative 2
  • Oxygen will be 2- except when bonded with fluorine
  • Fluorine is always negative 1
  • Group 17 will be negative 1
  • Metals will be positive
  • Nonmetals will be negative (except when bonded with other nonmetals)
  • The sum of the charges of the ions of a compound must equal zero
  • Some possible charges of elements can be found on your periodic table of elements. It is the number on the right side, second from bottom in each square for each element.

Polyatomic Ions
  • many-atomed ion that acts as a single charged unit
  • List of those polyatomic ions you must know:
    1. Ammonium NH4+
    2. Acetate C2H3O2
    3. Bromate BrO3
    4. Chlorate ClO3
    5. Hydroxide OH
    6. Iodate IO3
    7. Nitrate NO3
    8. Permanganate MnO4
    9. Thiocyanate SCN
    10. Carbonate CO32
    11. Chromate CrO42
    12. Dichromate Cr2O72
    13. Sulfate SO42
    14. Thiosulfate S2O32
    15. Phosphate PO43
When using polyatomics and you need more than one of the polyatomic ion, you must place it in ( ) and add the subscript to the outside of the ( )

           Ca2+  and  CO32    =     CaCO3                          Ba2+  and  OH   =   Ba(OH)2