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Oxidation-Reduction Reactions

Oxidation-Reduction Reactions. What are they?. Reactions with a loss and a gain of electrons among the reactants Oxidation Loss of electrons Most metals are oxidized Reduction Gain of electrons Most nonmetals are reduced. Oxidizing and Reducing Agents.

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Oxidation-Reduction Reactions

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  1. Oxidation-Reduction Reactions

  2. What are they? • Reactions with a loss and a gain of electrons among the reactants • Oxidation • Loss of electrons • Most metals are oxidized • Reduction • Gain of electrons • Most nonmetals are reduced

  3. Oxidizing and Reducing Agents • What is oxidized acts as a reducing agent • With the loss of electrons, the oxidation number increases • This gives a positive charge • What is reduced acts as an oxidizing agent • With the gaining of electrons, the oxidation number decreases • This results in a negative charge

  4. Electronegativity Review • Defined as: an element’s tendency to gain electrons

  5. Rules for Determining Oxidation Numbers • Rule 1: The oxidation number of an uncombined atom is zero • Examples: Ca, S, H2, N2, O2 all would have oxidation numbers of zero (n = 0)

  6. Rules for Determining Oxidation Numbers • Rule 2: The oxidation number of a monoatomicion is equal to the charge of the ion • Examples: • Calcium ion, Ca+2 has an oxidation number, n = +2 • Bromide ion, Br-1 has an oxidation number, n = -1

  7. Rules for Determining Oxidation Numbers • Rule 3: The oxidation number of the more electronegative atom in a molecule is the same as the charge it would have if it were an ion • Examples: • N in NH3 has a charge of -3 • O in NO2 has a charge of -2

  8. Rules for determining oxidation numbers • Rule 4: The oxidation numbers of group 1 and 2 metals and aluminum are positive and equal to their number of valence electrons • Examples: • Na has an oxidation number of +1 • Mg has an oxidation number of +2 • Al has an oxidation number of +3

  9. Rules for determining oxidation numbers • Rule 5: The oxidation number of oxygen is always -2 except in peroxides, such as hydrogen peroxide (H2O2), where it is -1

  10. Rules for determining oxidation numbers • Rule 6: The sum of the oxidation numbers in a neutral compound is always zero • Example: • CaBr2 (+2) + 2 (-1) = 0

  11. Rules for determining oxidation numbers • Rule 7: The sum of the oxidation numbers of the atoms in a polyatomic ion or compound with a charge is equal to the charge • Example: • NO3- = (+5) + 3(-2) = -1

  12. Sample Problems • Determine the oxidation number for each of the elements in the following: • KClO3 • K: n = • Cl: n = • O: n = • SO42- • S: n = • O: n =

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