Electrochemistry Part 1

Question 1

Define oxidation number

Answer 1

Total number of electrons that an atom gains or loses in order to from a chemical bond with another atom.

Question 2

What are the 5 rules of oxidation numbers?

Answer 2

1. Free elements have an oxidation number of 0, e.g. Na, Au, H2, S8
2. Sum of oxidation numbers in a compound is equal to 0, e.g. NaCl
3. Sum of oxidation numbers in polyatomic ion is equal to the charge of that ion, e.g. SO4 2- : oxidation number of sulfur + oxygen should be -2
4. Some group numbers are fixed:

Group 1 = +1
Group 2 = +2
Fluorine = -1
Hydrogen with non-metal = +1
Hydrogen with metal (or Boron) = -1
Oxygen = -2 (Except in H2O2 where it is -1 or if bonded to fluorine)

5. Group 7 = -1 (Except Cl, Br, and I when bonded to O and F)

Question 3

What elements have varying oxidation numbers?

Answer 3

Nitrogen
Phosphorous
Chlorine
Sulfur
Oxygen (In the case of H2O2 and Na2O2)
Hydrogen (+1 if bonded to non-metal and -1 if bonded to metal)
All transition metals