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For Chemistry with Mrs.Weeks at TPS

Oxidation Number

The charge that an atom in a molecule would develop if the most electronegative atoms in the molecule took the shared electrons from the less electronegative atoms

Oxidation numbers treat all compounds as


Oxidation numbers

aren't real

Oxidation numbers do not

have any significance in the real world

The sum of all oxidation numbers

in a molecule must equal the charge of that molecule

Rule #1

When a substance has only one type of atom, the oxidation number for that atom = the charge of the substance divided by the number of atoms present

Rule #2

Group 1A metals always have a +1 O. # in molecules that have more than 1 type of atom

Rule #3

Group 2A metals always have a +2 O. # in molecules that have more than 1 type of atom

Rule #4

Fluorine always has a -1 O. # in molecules that have more than 1 type of atom

Rule #5a

When with 1 other atom that is a metal, H has a -1 O. #

Rule #5b

When with other multiple atoms, H has a +1 O. #

Rule #6

Oxygen has an -2 O.# in molecules that have more than 1 type of atom

Rule #7

If all else fails, apply the O. # as the same as what the atom would take in an ionic compound. Groups 3A, 6A and 7A work best.


the process by which an atom loses electrons


the process by which an atom gains electrons

LEO says GER

lose electrons oxidation, gain electrons reduction

when an atom undergoes reduction

we say that it has been reduced

when an atom undergoes oxidation

we say that it has been oxidized

If any 2 atoms change oxidation numbers in a reaction

it is a redox reaction


is just electrons traveling through a wire


indicates the voltage of a battery

salt bridge

cancels out + or - charge that develops in an anode or cathode

a salt bridge contains

an aqeuous ionic compound and is necessary for the proper working of the battery


negative side of the battery


positive side of the battery


negative ions


source of positive charges

galvanic cell

battery as described in Module 16

metal strips conducting electrons


Lead-acid battery

car battery

in lead acid battery, reactants

PbO2, Pb and H2SO4 (aq)

in lead acid battery, products

PbSO4, H2O

when you recharge a battery,

you reverse the reaction, converting produscts to reactant

dry cell battery

contains no aqueous solutions

dry cell battery used in flashlights

alkaline cell because the salt bridge uses KOH, a base

in alkaline batteries, the inner construction of the battery is broken down

which means it can not recharge

redox reactions are often useful,

but can be harmful (rust, corrosion)

corrosion is


use the 7 rules of determining ox. numbers as a


what happened in exp. 16.1

citric acid oxidized iodine to 5+ in order to form the blue starch compound, it needed to be 0

anodes go on the


cathodes go on the


car battery is


dry cell battery

no aq solution

the anode must be made of

metal in equation

cathode does not need to be made of

metal in equation


+ ions


- ions

all batteries are not

galvanic cells

h2so4 is a reactant

in a lead acid battery

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