1. The oxidation and reduction states of elements
Redox
The oxidation and reduction states of elements

2. Oxidation Oxidation is the loss of an electron
Oxidizing agent – oxidizes other atoms, is reduced in the process
Oxygen
Powerful oxidation agent
Not involved in ALL oxidations, just considered to be one the main culprits.

3. Reduction
Reduction agent – reduces other atoms, is oxidized in the process
Reduction is the gain of an electron

4. O.I.L.R.I.G. OIL RIG OXIDATION IS LOSING ELECTRONS REDUCTION
GAINING ELECTRONS

5. Oxidation Number S S S S S S S S
Atoms by themselves have an oxidation number of 0
This is true even for diatomic and larger monospecific (same element) elements such as H2 and S8
When in a polyatomic molecule elements typically will have a standard oxidation number based upon the electronegativity of the element. S S S S S S S

6. Oxidation Number S S S S S S S S
Higher Electronegativity – the lower the oxidation number
Oxygen – Upper right of periodic table – high oxidation number – normally 2-
Cesium – Lower left of periodic table – low oxidation number – normally 1+ S S S S S S S

7. Oxidation Number
Monoatomic and Polyatomic Ions normally keep their charge. K+
Cl-
Oxygen is always 2- except
O2 both atoms are 0
And peroxides such as H2O2 where O is 1-
Hydrogen is almost always 1+ except when it combines with an alkaline metal where it is -1 and H2 where it is 0
Florine is always -1
The combined oxidations numbers will always equal 0 for a neutral compound or the ionic charge for a polyatomic ion.

8. Oxidation Trends – Periodic Table

9. Oxidation States-
Oxidation State – the oxidation number of an atom in a chemical bond.
Very similar to Ionic Charges
Exists in both covalent and ionic bonds. H O Na Cl

10. Oxidation States in Formula
O H2  2 H2O
Oxygen oxidizes Hydrogen and gains 2 electrons.
Hydrogen Reduces Oxygen and looses 2 electrons.
Oxygen is 2-
Each Hydrogen is 1+

11. Oxidation without Oxygen
Even without oxygen – oxidation can occur
Oxidation could mean – acting like oxygen would
F2 + H2  2 HF
Here – Oxygen is not present –
Hydrogen looses electrons and Fluorine gains electrons H F

12. Redox Redox Reduction + Oxidation
These reactions are considered “redox” (“red”uction + “ox”idation)
They do not happen in isolation.
Reduction + Oxidation
Redox

13. Determining oxidation numbers for elements without rules.
Nonspecific oxidation numbers
Based on the whole charge of the compound or polyatomic ion.
NO(g) has O = -2
N = +2.
NO2(g) has O = -2 * 2 = -4
N = +4.
SO42- has O = -2.
S + 4(-2) = -2
Solving the equation gives S = = +6.
K2Cr2O7 has K = +1 and O = -2.
2(+1) + 2 Cr + 7(-2) = 0; 2 Cr = 12; Cr = +6.

14. Determine the charges for the elements in the below compounds
Determine the charges for the elements in the below compounds. List in your notes.
1. N in N2O3
2. S in H2SO4
4. C in CO
5. Na in NaCl
6. H in H2O
7. Ba in BaCl2
8. N in NO2-