Determine oxidation numbers for elements in chemical compounds
Enter formula with capital letters for elements
0 for neutral compounds, positive or negative for ions
The oxidation state calculator determines the oxidation number for each element in a chemical compound by applying oxidation state rules. It uses known oxidation states of common elements and the principle that oxidation states must sum to the total charge to solve for unknown oxidation numbers.
Σ(oxidation numbers) = total charge
Identify Known States
H = +1, O = -2 (by rules)
Set Up Equation
2(+1) + S + 4(-2) = 0 (neutral compound)
Solve for S
2 + S - 8 = 0 → S = +6
Result
H₂SO₄: H = +1, S = +6, O = -2
Confusing with formal charge
Oxidation state ≠ formal charge or actual charge
Forgetting peroxide exception
O in H₂O₂ is -1, not -2
Wrong sum for ions
Polyatomic ions sum to ion charge, not 0
Ignoring subscripts
Must multiply oxidation state by subscript
Oxidation state (oxidation number) is the hypothetical charge an atom would have if all bonds were completely ionic. It's a bookkeeping method to track electron transfer in redox reactions. For example, in H₂O, H has oxidation state +1 and O has -2.
Apply rules in order: (1) Free elements = 0, (2) Monatomic ions = charge, (3) H = +1 (usually), (4) O = -2 (usually), (5) Group 1 = +1, (6) Group 2 = +2, (7) F = -1 always. Then solve algebraically so the sum equals total charge.
Charge is the actual electrical charge on an ion (e.g., Na⁺ has +1 charge). Oxidation state is a formalism for covalent compounds assuming all electrons go to the more electronegative atom. In ionic compounds they're equal, but in covalent compounds they differ.
Yes, average oxidation states can be fractional in compounds where the same element exists in multiple oxidation states. For example, Fe₃O₄ contains Fe²⁺ and Fe³⁺, giving an average of +8/3. However, individual atoms have whole number states.
Oxidation is loss of electrons (increase in oxidation state). Reduction is gain of electrons (decrease in oxidation state). Mnemonic: OIL RIG (Oxidation Is Loss, Reduction Is Gain) or LEO GER (Loss of Electrons = Oxidation, Gain of Electrons = Reduction).
Oxygen is highly electronegative (second only to fluorine) and readily gains 2 electrons to achieve a stable octet. Exceptions: peroxides (O₂²⁻, oxidation state -1), superoxides (O₂⁻, -1/2), and when bonded to fluorine (OF₂, +2).
For main group elements, maximum oxidation state typically equals group number (e.g., S in Group 16 can reach +6). Minimum is often (group number - 8) for nonmetals (e.g., S can be -2). Transition metals can have variable oxidation states.
Redox Reactions
Identifying oxidizing and reducing agents
Equation Balancing
Balancing redox equations
Electrochemistry
Battery and fuel cell reactions
Analytical Chemistry
Titrations and analysis