Ch.4 - Chemical Quantities & Aqueous ReactionsWorksheetSee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds
Jules Bruno

The oxidation number, also known as oxidation state, represents the number of electrons that an element can either gain, lose or share to form a chemical bond with another element. 

Oxidation Number 

By definition, the oxidation number can be seen as the potential charge an atom can possess from either the sharing, gaining or loss of electrons in an oxidation-reduction reaction. 


Calculating Oxidation Number

In order to calculate the oxidation of an element or compound we can utilize the following rules. 


Rule 1: For an atom in its standard or elemental state its oxidation number is equal to zero. The following elements and molecules are good examples. 

C (graphite)              O2 (g)              P4 (s)              Cl­2 (g)             He (g)             Zn (s)


Rule 2: For an ion, its charge is equal to its oxidation number. 

Na+  Oxidation Number = +1                     SO42–  Oxidation Number = – 2


Rule 3: For metals from Group 1A, their oxidation number is equal to +1 when connected to other elements.

Oxidation Number (Group 1A)


Rule 4: For metals from Group 2A, their oxidation number is equal to +2 when connected to other elements. 

Group-2A-Oxidation-Numbers-ListOxidation Numbers (Group 2A)


Rule 5: For hydrogen, the oxidation number is +1 when connected to non-metals and -1 when connected to boron or a metal. 

Oxidation Numbers (Hydrogen)


Rule 6: For fluorine, the oxidation number is -1 when connected to other elements. 

Fluorine-Oxidation-State-RulesOxidation Number (Fluorine)


Rule 7: For oxygen, the oxidation number is -1 when it’s a peroxide, -1/2 when it’s a superoxide and -2 in most other cases. 



Peroxide 

A peroxide represents a compound containing two elements from Group 1A bonded to two oxygen atoms. 

Oxidation-Number-PeroxidesOxidation Number (Peroxides)


Superoxide 

A superoxide represents a compound containing one element from Group 1A bonded to two oxygen atoms. 

Oxidation-Number-SuperoxidesOxidation Number (Superoxides)


Rule 8: For the halogens (Cl, Br, I), their oxidation numbers are -1 unless they are connected to oxygen. 

Oxidation-Number-HalogensOxidation Number (Halogens)


When the halogen (Cl, Br, I) is connected to oxygen then the oxidation number must be calculated. 

Calculating-Oxidation-Number-PerbromateCalculating Oxidation Number (Perbromate Ion)


Now let’s take a look at a few practice problems. 


PRACTICE 1: Determine the oxidation number of the sulfur atom in the sulfate ion. 

Calculating-Oxidation-State-SulfateCalculating Oxidation State (Sulfate Ion)


PRACTICE 2: Determine the oxidation number of the nitrogen atom. 

Calculating-Oxidation-Number-AmmoniumCalculating Oxidation Number (Ammonium Ion)


PRACTICE 3: Determine the oxidation number of the carbon atom in carbon dioxide. 

Calculating-Oxidation-Number-CO2Calculating Oxidation Number (Carbon dioxide)


Beyond Oxidation Numbers

Oxidation Numbers can serve roles beyond redox reactions such as naming ionic compounds, determining the degree of oxidation within biological reactions, understanding electron configurations and other trends of the periodic table. 


Jules Bruno

Jules felt a void in his life after his English degree from Duke, so he started tutoring in 2007 and got a B.S. in Chemistry from FIU. He’s exceptionally skilled at making concepts dead simple and helping students in covalent bonds of knowledge.