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Redox Rules!

Learn about the rules of oxidation numbers and electronegativity in order to understand the formation of ionic and covalent bonds. Explore the definition of electronegativity, the trends in electronegativity values, and the rules for assigning oxidation numbers to atoms and ions. Discover exceptions to these rules and how to identify oxidizing and reducing agents in chemical reactions.

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Redox Rules!

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  1. Redox Rules! Redox Rules to Learn For Ionic and Covalent bonds

  2. Electronegativity and Redox Rules • Definition: Electonegativity is the atom’s ability to attract electrons. • Fluorine is the most electronegative element

  3. Electronegativity Trend Increase EN More protons to attract electrons Decrease EN electrons get further away from protons

  4. Rule #1 Oxidation number of an uncombined atom = zero (no compounds or ions) i.e . Mg, H2, Na ie. All H2 O2 N2 Cl2 Br2I2F2 ’s ox. # are zero 0 0 0 0 0 0 0 0 0 0

  5. Rule #2 Oxidation number of a monatomic ion = charge of the ion i.e. Mg2+ , O2- , Al3+ , Br- -2 +3 -1 +2

  6. Rule #3 The sum of the oxidation numbers of a neutral compound = 0 i.e. H2O CO2 CO NaCl +1 -1 -2 -2 +1 +4 +2 -2 2(+1) 2(-2) = 0 =0 =0 - 2 = 0 4 +

  7. Rule #4 The oxidation number for H is +1 Exception: when bonded to a less electronegative element (metal), then it is -1. i.e. LiH, NaH, MgH2 Exception i.e. HF, HCl -1 +1 -1 +1 +2 -1 -1 +1 -1 +1

  8. Rule#5 Oxygen’s oxidation number is -2, in a compound Two exceptions: peroxides and fluorine in H2O2 with OF2 +1 ? = -1 where O is -1 2(+1) + 2( ?) = 0 +2 -1 where O is +2 2(-1) ? + = 0 fluorine (more electronegative)

  9. Rule#6 Oxidation number of polyatomic compound = zero polyatomic ion = the charge of the ion i.e. compounds: NH3 SiCl4 K3PO4 i.e. ions: NH4+ CO32- SO42- NO3- +1 -3 3(+1) -3 + = 0 +1 -3 4(1) -3+ = +1

  10. Rule#7 Oxidation numbers for metals in: Group 1A metal compound +1 2A metal compound +2 3A Aluminum compound +3 i.e. NaCl MgSO4 AlPO4 +3 +6 -2 +2 -1 +1 +2 + ? + 4(-2) = 0 = 0 = 0

  11. Rule #8 • The most electronegative element fluorine ALWAYS has an oxidation number of -1 when it is bonded to another element. • i.e. HF

  12. Question Time • Assign oxidation numbers to each element • Cl2 • Cl- • MgCl2 • NaH • HCl • K3PO4 • CaSO4 • KF

  13. Using the Rules Oxidation Number • If oxidation number goes up it is oxidized. • If oxidation number goes down it is reduced.

  14. Using the Rules-Last Lesson Balance the reactions, write the oxidation numbers for each atom and write the oxidizing and reducing agents. Ex1 HCl + Zn  ZnCl2 + H2 Loss of electron oxidation (LEO) Reducing agent 0 +2 -1 0 -1 +1 2 +2 + =0 2(-1) Gain of electron reduction (GER) Oxidizing agent

  15. Using the Rules Ex2 Mg + N2 Mg3N2 Ex3 H2S + Cl2  HCl + S Ex4 Fe + O2  Fe2O3

  16. Summary of Oxidation/Reduction • There are three definitions of oxidation and reduction: • Oxidation Reduction 1. 1. 2. 2. 3. 3. Gaining of electrons (GER) Losing of electrons (LEO) Decreasing oxidation # Increasing oxidation # Gaining oxygen Losing oxygen

  17. Two ways to remember oxidation/reduction (redox) is: L E O goes G E R O I L R I G XIDATION S EDUCTION L E C T R O N S EDUCTION L E C T R O N S O S E XIDATION AIN OSING S AINING

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