Oxidation numbers

The oxidation number of an atom is the charge that the atom appears to have when the electrons are distributed according to certain rules...RULES:-In free elements .e.g N2, each atom has an oxidation number of 0.The sum of the oxidation numbers of all the atoms in a molecule is 0.The oxidation number of a simple ion containing one atom is equal to the charge on the ion e.g. oxidation number of Cl- = -1The sum of all the oxidation numbers of all the atoms in a complex ion is equal to the charge on the ion e.g. a nitrate ion (NO3-) where nitrogen has an oxidation number of +5 and oxygen has an oxidation number of -2, the oxidation number adds up to -1.Hydrogen has an oxidation number of +1 in its compounds EXCEPT in metallic hydrides where it is -1.Oxygen has an oxidation number of -2 in its compounds EXCEPT in hydrogen peroxide where it is -1 (H2O2), and when bonded to fluorine it is +2.The oxidation number of a group 1 element in its compounds is always +1, and of the group 2 elements is always +2.The oxidation number of a halogen when bonded to a less electronegative atom is -1 (Fluorine is the most electronegative element, and ALWAYS has an oxidation number of -1 in its compounds)Chlorine has an oxidation number of -1 in compounds where it is not bonded to oxygen or fluorine.

OXIDATION STATESOxidation numbers represent the oxidation state of an element e.g. group 1 and group 2 have just on oxidation state (1 and 2 respectively). Oxygen has usually just on oxidation state.The halogens, in their compounds, with the exception of fluorine, have several oxidation states.

Naming of transition metal compounds.Oxidation numbers are used when naming compounds of transition metals symmetrically.In the case of a compound containing two elements only, the ending -ide is used, and the oxidation number is indicated by a roman numeral in brackets after the name of that metal e.g. copper (II) chloride.If the compound contains a complex ion e.g. CuNO3, then the name ends with the name of the complex ion - copper (I) nitrateIf the compound contains water or crystallisation, the number of molecules of water of crystallisation is indicated at the end of the name e.g. CuSO4.5H2O - copper (II) sulfate - 5 - water.

OXIDATION AND REDUCTION IN TERMS OF OXIDATION NUMBERS....Oxidation is an increase in oxidation numberReduction is a decrease in oxidation number.*When calculating oxidation numbers, te oxidation number for only a single atom of each element should be written.EVERYDAY EXAMPLES OF OXIDISING AND REDUCING AGENTSBleaching is a redox reaction. Many domestic bleaches contain sodium hypochlorite (NaOCl) This is an example of an oxidising bleachNaOCl ---> NaCl (reduced to sodium carbonate)Reducing bleaches include sodium sulfite (Na2SO3) used  in the paper industry and sulfur dioxide (SO2) used in solution where it forms sulfite ions (SO3 2-) When sulfite ions bleach by reduction, they are reduced to sulfate ions:SO3 2- --> SO4 2-

Oxidation numbers

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