Procedure for Calculation of Oxidaton Number

By applying the above rules, we can calculate the oxidation numbers of elements in the molecules/ions by the following steps.

(i) Write down the formula of the given molecule/ion leaving some space between the atoms.

(ii) Write oxidation number on the top of each atom. In case of the atom whose oxidation number has to be calculated write x.

(iii) Beneath the formula, write down the total oxidation numbers of each element. For this purpose, multiply the oxidation numbers of each atom with the number of atoms of that kind in the molecule/ion. Write the product in a bracket.

(iv) Equate the sum of the oxidation numbers to zero for neutral molecule and equal to charge on the ion.

(v) Solve for the value of x.

Table: Oxidation number of some elements in compounds, ions or chemical species

Element	Oxidation Number		Compounds, ions or chemical species
Sulphur (S)	– 2		H2S, ZnS, NaHS, (SnS3)2–, BaS, CS2
	0		S, S4, S8, SCN–
	+ 1		S2F2, S2Cl2
	+ 4		SO2, H2SO3, (SO3)2–, SOCl­2, NaHSO3, Ca[HSO3]2, [HSO3]–,SF4
	+ 6		H2SO4, (SO4)2-, [HSO4]–, BaSO4, KHSO4, SO3, SF6­­­­, H2S2O7, (S2O7)2–
Nitrogen (N)	– 3		NH3, (NH4)+, AlN, Mg3N2, (N)3–, Ca3N2, CN–
	– 2		N2H4, (N2H5)+
	– 1		NH2OH
	–1/3		NaN3, N3H
	0		N2
	+ 1		N2O
	+ 2		NO
	+ 3		HNO2, (NO2)–, NaNO2, N2O3, NF3
	+ 4		NO2
	+ 5		HNO3, (NO3)–, KNO3, N2O5
Chlorine (Cl)	– 1		HCl, NaCl, CaCl2, AlCl3, ICl, ICl5, SOCl2, CrO2Cl2, KCl, K2PtCl6, HAuCl4, CCl4HHHhhhhkkkkkk
	0		Cl, Cl2
	+ 1		HOCl, NaOCl, (OCl)–, Cl2O
	+ 3		KClO2, (ClO2)–, HClO2
	+ 4		ClO2
	+ 5		(ClO3)–, KClO3, NaClO3, HClO3
	+ 7		HClO4, Cl2O7, KClO4, (ClO4)–
Hydrogen (H)	– 1		NaH, CaH2, LiAlH4, LiH
	+ 1		NH3, PH3, HF
Phosphorus (P)	– 3		PH3, (PH4)+, Ca3P2
	0		P4
	+ 1		H3PO2, KH2PO2, BaH4P2O4
	+ 3		PI3, PBr3, PCl3, P2O3, H3PO3
	+ 5		(PO4)3–, H3PO4, Ca3(PO4)2, H4P2O7, P4O10, PCl5, (P2O7)4–, Mg2P2O7, ATP
Oxygen (O)	– 2		H2O, PbO2, (CO3)2–, (PO4)2–, SO2, (C2O4)2–, HOCl, (OH)–, (O)2–
	– 1		Na2O2, BaO2, H2O2, (O2)2–, Peroxides
		– 1/2		KO2
		0		O, O2, O3
		+ 1		O2F2
		+ 2		OF2
Carbon (C)		– 4		CH4
		– 3		C2HHHhhhhjkjkkkH6
		– 2		CH3Cl, C2H4
		– 1		CaC2, C2H2
		0		Diamond, Graphite, C6H12O6, C2H4O2, HCHO, CH2Cl2
		+ 2		CO, CHCl3, HCN
		+ 3		H2C2O4, (C2O4)2–
		+ 4		CO2, H2CO3, (HCO3)–, CCl4, Na2CO3, Ca2CO3, CS2, CF4, (CO3)–2
Chromium (Cr)		+ 3		Cr2(SO4)3, CrCl3, Cr2O3, [Cr(H2O)4Cl3]
		+ 6		K2CrO4, (CrO4)2–, K2Cr2O7, (Cr2O7)2–, KCrO3Cl, CrO2Cl2, Na2Cr3O10, CrO3
Manganese (Mn)		+ 2		MnO, MnSO4, MnCl2, Mn(OH)2
		+ 8/3		Mn3O4
		+ 3		Mn(OH)3
		+ 4		MnO2, K2MnO3
		+ 6		K2MnO4, (MnO4)2–
		+ 7		KMnO4, (MnO4)–, HMnO4
Silicon (Si)		– 4		SiH4, Mg2Si
		+ 4		SiO2, K2SiO3, SiCl4
Iron (Fe)				Fe3O4
		+ 2		FeSO4. (NH4)2SO4 (Ferrous ammonium sulphate), K4Fe(CN)6, FeCl2
		+ 3		K3[Fe(CN)6], FeCl3
Iodine (I)		+ 7		, KIO4
Osmium (Os)		+ 8		OsO4
Xenon(Xe)		+ 6		XeO3, XeF6

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