Oxidation and Reduction

OXIDATION	REDUCTION
Combination with oxygen	Removal of oxygen
C + O₂ à CO₂ carbon is oxidized	2 HgO à 2Hg + O₂mercury is reduced
Loss of electrons	Gain of electrons
Fe à Fe³⁺ + 3 e^-iron is oxidized	Zn²⁺ + 2e^- à Zn zinc ion is reduced
Algebraic increase in oxidation number [becomes more positive]	Algebraic decrease in oxidation number [becomes more negative]
2KClO₃ à 2 KCl + 3O₂ the oxidation number of O goes from -2 to 0 oxygen is oxidized	PbO₂ + Mg à PbO + MgO the oxidation number of Pb goes from +4 to +2 lead is reduced 2KClO₃ à 2 KCl + 3O₂ the oxidation number of Cl goes from +5 to -1 chlorine is reduced
Removal of hydrogen atoms	Addition of hydrogen atoms

Oxidation and reduction always occur together!
The redox reaction: 2“H₂” + O₂ à 2H₂O is our major source of energy!

“Hydrogen” Comes in Many Guises

Representation	Description
H₂	H:H, H-H molecular hydrogen, a diatomic molecule consisting of two hydrogen nuclei [protons] joined by a s_1s-1s single covalent bond containing two electrons
“H₂”	molecular hydrogen or any of its equivalents listed below
2H⁺ + 2 e^-	two protons and two electrons
2H•	two hydrogen atoms
H• + H⁺ + e^-	hydrogen atom and a proton and an electron
H:^- + H⁺	hydride ion and a proton
SubH₂	substrate with two removable hydrogens