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Oxidation & Reduction Reactions

Oxidation & Reduction Reactions. Section 1. Oxidation-reduction reactions involve a transfer of electrons Oxidation involves the loss of electrons Reduction involves the gain of electrons. Oxidation States.

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Oxidation & Reduction Reactions

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  1. Oxidation & Reduction Reactions Section 1

  2. Oxidation-reduction reactions involve a transfer of electrons • Oxidation involves the loss of electrons • Reduction involves the gain of electrons

  3. Oxidation States • An oxidation number is assigned to an element in a molecule based on the distribution of electrons in that molecule • Rules for assigning oxidation numbers

  4. Oxidation States (cont.)

  5. Oxidation • Processes in which the atoms or ions of an element experience an increase in oxidation state are oxidizing processes • 2Na + Cl2 2NaCl • Each sodium atom loses an electron changing the oxidation state from 0 to +1 • An element whose oxidation number increases is oxidized • Na is oxidized

  6. Reduction • Processes in which the atoms or ions of an element experience an increase in oxidation state are oxidizing processes • 2Na + Cl2 2NaCl • Each chlorine atom accepts an electron changing its oxidation state from 0 to -1 • An element that undergoes a decrease in oxidation state is reduced • Cl is reduced

  7. Redox as a Process • Just like mass has to be conserved in reactions, so does the number of electrons • This means that for oxidation to occur, reduction must also occur • Any chemical process in which elements undergo changes in oxidation number is an oxidation-reduction reaction • Or redox reaction for short

  8. Redox as a Process (cont.) • The redox reactions can be written showing either just the oxidation, or just the reduction alone • These are called half-reactions • 3Na  3Na+ + 3e- (oxidation) • Al3+ + 3e- Al (reduction) • 3Na + Al3+  3Na+ + Al (redox reaction)

  9. If none of the atoms in a reaction change oxidation state, the reaction is not a redox reaction • SO2 + H2O  H2SO4 • Na+ + Cl- + Ag+ + NO3-  Na+ + NO3- + AgCl

  10. Redox Reactions & Covalent Bonds • Oxidation numbers are assigned based on the electronegativity of an atom relative to the other atoms to which it is bonded in a molecule • It is not based on a real charge

  11. Redox in Covalent Bonds (cont.) • When hydrogen burns with chlorine, a covalent bond forms from the sharing of two electrons • The electrons in the bond are not shared equally and are more strongly attracted to the chlorine. Why? • H2 + Cl2 2HCl • Use the oxidation rules to assign the oxidation numbers

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