Oxidation states or oxidation numbers

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  • 1. Oxidation StatesOxidation Numbers

2. Learning Objectives: Students will be able to1. define oxidation state.2. learn the rules for assigning oxidation states. 3. explain redox in terms of oxidation states.4. use of oxidation states in nomenclature.5. learn the advantages of oxidation states. 3. Oxidation State Or NumberMany redox reactions involve a complete transfer of electrons from one substance to another.These redox processes usually have ions aseither the reactants Q| :_p. mducts.In some cases, the reactants and products are both ions. There are,however,some reactions which are regarded as redox processes in spite of the fact that they involve only molecules and do not have complete transfer of electrons from onesubstance to another.Animation 4. Animation For example,the reactions2__H2+Q2 -I _2H2O-an: -__. and.C/ -(9% 202 -*3 (oz + 2;/ toc+o2 co; *%-- clearly involve redox,yet there is no complete transfer of electrons from one substance to another. In orderto overcome this problem,the concept of Oxidation states ( or Oxidation Numbers) wasintroduced.This provided a similar,but_altemative,definition of redox to that involving electron transfer. 5. Definition of oxidation state: "The formal charge on an atom in a compound or an ion is called oxidation statelt ma ed as. ""'The number of charges an atom would have in a molecule or ion if elec rons weretransferred completely".juj 6. 0 O .Eor example:Ma +. (. _EUsing oxidation numbers it is possible to decide whether redox has occurred in processes involvingeither transfer or reshaping of electrons.2..11- '1;> MI;o(2_The oxidation numbers of the atoms in uncombined elements are given an oxidationnumb. eL0.f. zero.Thus,the oxidation number of l_llg jsjl,as is the oxidation number of chlorine atoms in Clz.For simple ions,the oxidation number is simply the charge on the ion.Thus,the oxidation number of C_. _l",_g2* and g? " are -1, +_2_and -_I; respectively. 7. Rules For Assigning Oxidation StateslNumbers: ' Guiding rules that have been established to determine the oxidation statelnumber of atoms are mentioned below: _s__1_. __T_he oxidation state of all the elements in freestate is zero. Br2os Nan:H209 P09 0201 N20 2. In a compound,the more electronegativeelements are assigned negative oxidation states,and the less electronegative elements are assigned the positive oxidation states. Cl*F",H*Cl" .