Oxidation Reduction Reaction (Redox):A reaction in which electrons are

transferred from one substance to another.

Oxidation cannot occur without reduction Definition of Oxidized:

1. Losing of electrons (LEO)2. Increasing the ox. number, ie: 0 to +1

-2 to -13. Gaining oxygen

Definition of Reduced:1. Gaining of electrons (GER)2. Reducing the ox. number, ie: -1 to -2

1 to 03. Losing oxygen

2Mg + O2 2MgO Mg atom transfers two electrons to each

oxygen atom. As a result 2 Mg atoms become Mg2+ and

two oxygen atoms become O2-

Mg loses two electrons O gains two electrons

2Mg + O2 2MgO Mg atom transfers two electrons to each

oxygen atom. As a result 2 Mg atoms become Mg2+ and

two oxygen atoms become O2-

Mg loses two electrons O gains two electrons

Can oxidation occur without reduction? What are the three definitions of oxidation? What are the three definitions of reduction? What is a way to remember oxidation/reduction in

terms of transfer of electrons? Does the oxidation number increase or decrease

when there is oxidation? Does the oxidation number increase or decrease

when there is reduction?

When an electron is lost (An electron is found on the product side) there is oxidation◦ X0 X+1 + e-

When an electron is gained (An electron is found on the reactant side) there is reduction◦ e- +Y+1 Y0

startfinish

Ex5 Na0Na+1

Ex6 Fe+3Fe+2

Ex7 N+1N+2

Ex8 Mg+2Mg0

+1e-

1e-+

+1e-

2e-+

(LEO)oxidized

(GER)reduced

(LEO)oxidized

(GER)reduced

Whatever is oxidized is called the reducing agent

Whatever is reduced is called the oxidizing agent

startfinish

Ex5 Na0Na+1

Ex6 Fe+3Fe+2

Ex7 N+1N+2

Ex8 Mg+2Mg0

+1e-

1e-+

+1e-

2e-+

oxidized

reduced

oxidized

reduced

reducing agent

oxidizing agent

reducing agent

oxidizing agent

What is a reducing agent?

What is a oxidizing agent?

Are metals generally oxidized or reduced?

Are nonmetals generally oxidized or

reduced?

Redox Rules to LearnFor Ionic and Covalent bonds

Definition: Electonegativity is the atom’s ability to attract electrons.

Fluorine is the most electronegative element

Increase ENMore protons to attract electrons

Decrease ENelectrons get further away from protons

Oxidation number of an uncombined atom = zero(no compounds or ions)

i.e . Mg, H2, Na

ie. All H2 O2 N2 Cl2 Br2 I2 F2 ’s ox. # are zero

0 0 0

0 0 0 0 0 0 0

Oxidation number of a monatomic ion = charge of the ion

i.e. Mg2+ , O2- , Al3+ , Br-

+2 +3 -1-2

The sum of the oxidation numbers of a neutral compound = 0

i.e. H2O CO2 CO NaCl+1

2(+1)

-2

- 2 = 0

-2

2(-2)

+4

4 + = 0

-2+2

=0

-1+1

=0

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

Oxygen’s oxidation number is -2, in a compound

Two exceptions: peroxides and fluorine

in H2O2

with OF2

+1

2(+1) + 2( ?) = 0

? = -1

where O is -1

-1

2(-1)? + = 0

+2 where O is +2

fluorine (more electronegative)

Oxidation number ofpolyatomic compound = zero polyatomic ion = the charge of the ion

i.e. compounds:

NH3 SiCl4 K3PO4

i.e. ions:

NH4+ CO3

2- SO42- NO3

-

+1

3(+1)

-3

-3 + = 0

+1

4(1)

-3

-3+ = +1

Oxidation numbers for metals in:

Group 1A metal compound +1 2A metal compound +2 3A Aluminum compound +3

i.e. NaCl MgSO4 AlPO4

+1 -1

= 0

+2 +3

= 0

-2

+2 + ? + 4(-2)

+6

= 0

The most electronegative element fluorine ALWAYS has an oxidation number of -1 when it is bonded to another element.

i.e. HF

Assign oxidation numbers to each element

1.Cl2

2.Cl-

3.MgCl2

4. NaH

5. HCl

6. K3PO4

7. CaSO4

8. KF

If oxidation number goes up it is oxidized. If oxidation number goes down it is reduced.

Balance the reactions, write the oxidation numbers for each atom and write the oxidizing and reducing agents.

Ex1 HCl + Zn ZnCl2 + H22-1+1 0 0-1

2(-1)

+2

+2 + =0

Loss of electron oxidation (LEO)

Gain of electron reduction (GER)

Oxidizing agent

Reducing agent

Ex2 Mg + N2 Mg3N2

Ex3 H2S + Cl2 HCl + S

Ex4 Fe + O2 Fe2O3

There are three definitions of oxidation and reduction:

Oxidation Reduction1. 1.

2. 2.

3. 3.

Losing of electrons (LEO)

Gaining oxygen

Increasing oxidation #

Losing oxygen

Decreasing oxidation #

Gaining of electrons (GER)

L E O goes G E R O I L R I G OSE

LECTRONS

XIDATION

AIN

LECTRONS

EDUCTION

XIDATION

S OSING

EDUCTION

S AINING