Chemistry Solution: Assigning Oxidation Numbers

Introduction

• Oxidation numbers are a bookkeeping system for tracking electrons in a compound.
• Important to note: oxidation numbers are not real charges on atoms.

Rules for Assigning Oxidation Numbers

1. Lone Elements: Oxidation number is zero.
   • Examples: Potassium (K), Aluminum (Al), O₂, S₈.
2. Electronegativity: Assign oxidation numbers starting with the most electronegative element.
   • Fluorine: Always -1.
   • Oxygen: Always -2 (except when bonded to fluorine).
3. Group Numbers: Oxidation numbers are based on the ion they would form:
   • Group 1A: +1
   • Group 2A: +2
   • Aluminum: +3
4. Hydrogen:
   • +1 when bonded to nonmetals.
   • -1 when bonded to metals.
5. Overall Charge: The sum of oxidation numbers must equal the overall charge of the compound.

Examples of Assigning Oxidation Numbers

Example 1: OF₂

• Fluorine: -1 (x2 for two fluorine atoms = -2 total).
• Oxygen: +2 (to balance the total sum to zero).
  • Final States: F = -1, O = +2.

Example 2: Iron(III) Oxide (Fe₂O₃)

• Oxygen: -2 (x3 for three oxygen atoms = -6 total).
• Iron: +3 (x2 for two iron atoms = +6 total).
  • Final States: O = -2, Fe = +3.

Example 3: Methane (CH₄)

• Hydrogen: +1 (x4 for four hydrogen atoms = +4 total).
• Carbon: -4 (to balance sum to zero).
  • Final States: H = +1, C = -4.

Example 4: Carbon Dioxide (Na₂CO₃)

• Oxygen: -2 (x3 for three oxygen atoms = -6 total).
• Sodium: +1 (x2 for two sodium atoms = +2 total).
• Carbon: +4 (to balance sum to zero).
  • Final States: O = -2, Na = +1, C = +4.

Conclusion

• The understanding of oxidation numbers is crucial for analyzing chemical compounds and reactions.
• Thank you for watching the Chemistry Solution tutorial!