The oxidation number of an element is a value that shows how many electrons an atom has lost, gained, or shared when forming a chemical compound or ion.
Key Points:
- It is like the “charge” an atom appears to have inside a molecule or ion.
- A positive oxidation number means the atom has lost electrons (oxidation).
- A negative oxidation number means the atom has gained electrons (reduction).
- For pure elements (like O₂, H₂, Na, Cl₂), the oxidation number is always 0.
- In ions, the oxidation number is the same as the ion’s charge.
Simple Examples in words:
- In sodium chloride, sodium has oxidation number +1 and chlorine has –1.
- In water, hydrogen is +1 and oxygen is –2.
- In carbon dioxide, oxygen is –2, so carbon must be +4.
In simple words: The oxidation number of an element tells us how “electron-rich” or “electron-poor” it is in a compound, helping us track redox reactions.