The "Rules"

    Several things that you have been introduced to in this course require you only to follow the rules, and you will get the answer right. It follows that you need to know these rules. Here they are in a concise format. Hopefully this will aid your studying.

Subject The Rules
Quantum numbers 1. The principal quantum number is n. n ³ 0.
2. The sub-shell number, or angular momentum number is l. l £ n-1.
3. The magnetis number, ml. -l £ ml £ +l.
4 The electron spin, ms. ms = +1/2 or -1/2.
Drawing Lewis structures 1. Count the valence electrons
2. Put the least electronegative element at the centre
3. Connect the terminal atoms to the central atom using single bonds (2 electrons each)
4. Complete the octets around the terminal atoms (not for H)
5. Put any remaining pairs on the central atom.
6. Move lone pairs from the terminal atoms to make multiple bonds wherever necessay to complete the octets of all atoms.
Predicting shapes via VSEPR 1. Draw the Lewis structure as outlined above
2. Count the bonds on the central atom (a double or triple bond counts as one bond). Count the lone pairs on the central atom.
3. Write the shorthand notation as, e.g., AX3E2, signifying one central atom (A), three terminal atoms (X3) and two lone pairs (E2).
4. Look up the corresponding shape. The table is on page 264-265 of the text. You need to know the names of the shapes by heart.
Hybridization To tell what kind of hybridization the central atom is using, you need to determine how many charge clouds (bonds plus lone pairs) there are around it, then use the following table:
Charge Clouds Hybridization

2

 sp
3 sp2

4

 sp3

5

 sp3d

6

 sp3d2
Predicting Oxidation Numbers (ON) 1. For an atom as the element, ON = 0.
2. For a monoatomic ion, ON = charge on the ion.
3. For oxygen in a compound, its ON = -2, usually.
4. In a covalent compound with a non-metal, H has ON = +1.
5. In other compounds, the element with the greater electronegativity gets a negative ON equal to its charge as an ion.
6. The sum of the ONs must equal the charge of the whole species.
Balancing REDOX reactions

1. Write the unbalanced reaction.
2. Write two unbalanced half-reactions.
    Then for each half reaction:
3. Balance for atoms other than H and O.
4. Balance O using H2O.
5. Balance H using H+.
6. Balance the charge using electrons.
7. Cross multiply and add half-reactions to make the electrons cancel.
8. Then, if necessary, to balance the reaction in a basic solution, add OH- to both sides such that the H+ on one side is cancelled out making water, leaving an excess of OH- on the other side.

Predicting which electrolytic reaction will occur The reaction with the more positive half-reaction potential will occur preferentially. Here, you need to ensure that the reaction is written as either an oxidation or reduction reaction as required, and that you have reversed the sign of the standard half reaction if necessary.
Nuclear reactions 1. The total number of nucleons (neutrons plus protons) is conserved.
2. The total charge is conserved.