Oxidation numbers and redox reactions

• OXIDATION NUMBERS:

  A measure of the number of electrons that an atom uses to bond with an atom of another element. Oxidation numbers are derived from a set of rules.
• OXIDATION NUMBERS:

  
  

  RULE 1

  The oxidation number of a neutral element is zero.

  
  

  For example: H2, F2, Na, O2 ,C(diamond)

  Because they are all elements, the oxidation states of the atoms is 0
• Oxidation number is also known as an element’s oxidation state.

  Oxidation numbers are book keeping numbers.

  
  

  They allow chemists to do things such as balance redox

  (reduction/oxidation) equations and determine molecular formulae.

  
  

  Oxidation numbers are positive or negative numbers, but don’t

  confuse them with positive or negative charges on ions or valences
• Oxidation number is a number assigned to an element in a compound that represents the number of electrons it has gained or lost to achieve its stable state. In covalent compounds, it indicates the sharing of electrons. For example, in$H_{2}O$, hydrogen has an oxidation number of +1, and oxygen has –2.
• If an atom receives 3 electrons from other atoms, its oxidation number would be -3 since it has gained electrons.
• To assign oxidation numbers, follow these rules:

  1. For elements in their free state, the oxidation number is 0.
  2. For monatomic ions, the oxidation number equals the charge.
  3. Fluorine always has –1.
  4. Hydrogen typically has +1.

  e.g., in$NaCl$, sodium has +1, and chlorine has –1.
• According to the oxidation number rules:

  • Fluorine always has an oxidation number of -1 (Rule 3)
  • Hydrogen typically has an oxidation number of +1 (Rule 4)

  So in$HF$,$F =$$-1$and$H =$$+$$1$. The key mistake was assigning fluorine a 0 oxidation number, which goes against its specific rule.
• RULES SIMPLIFIED:

  Rule 1: Free Atom Rule

  • When an atom is alone and happy, its name tag says "0"
  • Example:$O_2$in the air has a "0" name tag

  🤝 Rule 2: Ion Rule

  • If an atom becomes a special character (ion), its name tag shows its charge
  • Example: Sodium (Na) becomes Na+ with a "+1" name tag

  🌟 Rule 3: Fluorine's Special Rule

  • Fluorine always wears a "-1" name tag
  • It's like the kid who always wants to take an extra toy

  🚀 Rule 4: Hydrogen's Rule

  • Hydrogen usually wears a "+1" name tag
  • It's like a kid who likes to give away a toy
• When an atom loses two electrons during a chemical reaction, its oxidation number increases by +2. This is because the loss of electrons results in the atom having a higher positive charge.