Teachers Guide
Redox
Overview
In this activity students determine what makes a chemical reaction a redox
reaction. They begin their exploration by investigating the role of
electronegativity as it relates to the distribution of electrons around an atom.
Students then explore how the shifting of electron density or wholesale
transferring of electrons during chemical reactions results in a redox reaction.
Finally students use oxidation state to determine what is oxidized and what is
reduced during a chemical reaction.
Learning Objectives
Students will be able to:
 Investigate how electronegativity can affect the distribution of shared
electrons between two atoms.
 Explain how the shape of the electron cloud is related to the
electronegativity of the atoms bonded together.
 Explore redox reactions that involve a shift in electron density as well as
full transfer of electrons between atoms.
 Use oxidation states to determine what happens when an atom is
reduced.
Prerequisite Knowledge
Students should already have a basic understanding of:
 Atomic structure
 Orbitals
 Balancing equations
Background Resources
 An introduction resource to redox chemistry-http://www.metasynthesis.com/webbook/15_redox/redox.php
 A real world connection showing a redox reaction in a zinc-copper cell:
http://www.wwnorton.com/college/chemistry/gilbert2/tutorials/interfa
ce.asp?chapter=chapter_18&folder=zinc_copper_cell
 http://chemmovies.unl.edu/chemistry/redoxlp/Redox000.html
Approximate time for lesson completion: 60 minutes
Activity Answer Guide
Page 1:
In our mitochondria there is a system of
proteins that constitute the electron
transport chain. How can you tell from its
name that the electron transport chain
must involve redox reactions?
If electrons are being transported from one
place to another then they must be
transferred from on atom to another atom,
which is the definition of redox where
something loses and something else gains
reactions.
2. Explain how the shape of the electron
cloud in the model indicated which
element had the highest and lowest
electronegativity.
If the electron cloud is distorted to be larger
or closer to on atom, then that atom will
have the larger electronegativity.
3. What would happen to the electrons in
the bond between a carbon and
hydrogen atom if you replaced the
hydrogen atom with an oxygen atom?
(b) The electrons would shift more toward
the oxygen atom.
Page 2:
1. What relationship do you see between
electronegativity and where electrons
tend to be found in relation to the two
atoms?
Atoms with higher electronegativity pull the
electrons closer to them (or at least cause
the probability of the electron location to be
closer to the atom with higher
electronegativity.)
2. Take a snapshot of an unbalanced
sharing of electrons and annotate the
image to indicate which atom has the
higher electronegativity.
4. Reset the electron cloud so that
electrons are evenly distributed between
the two atoms. Then set one atom to
oxygen and one atom to hydrogen. Press
run and observe the resulting
distribution of electron charge. Based on
the definition of oxidation and reduction
select the correct answer below.
(e) Both A and D. The oxygen atom is
oxidized and the hydrogen atom is reduced.
Page 4:
1. Which metal has the strongest
attraction for electrons?
(a) silver
2. In the case where copper metal is put
into silver nitrate solution what is
reduced?
(a ) silver
Page 3:
1. Which element that you tested with the
model has the highest electronegativity?
(e) flourine
3. Explain how you know which metal
has the strongest attraction for electrons,
using observations of the model
behavior.
If there is a reaction where an ion from
solution "sticks" to the metal, causing the ion
to lose its positive charge by attracting
electrons from the metal, then that ion grabs
electrons better than the metal from which it
took electrons. As the ion takes electrons
one of the metal atoms loses electrons and
becomes an ion, going into solution. The
one that took the electrons must have the
stronger attraction.
(b) oxygen (O)
4. Observe the way the electrons get
redistributed in the reaction above.
Which element is oxidized?
Page 5:
(a) nitrogen (N)
1. Reduction occurs when there is a
change to a more negative oxidation
state. Which elements in the reactions
above are reduced? (CHECK ALL THAT
APPLY)
(b) oxygen
(e) silver
2. What happens to the electrons when
an atom is reduced? Use a specific
example from the reactions above and
explain how you know.
When an atom is reduced it is either pulling
electrons more toward itself like oxygen
does in the acetylene burning reaction, or it
gains electrons from another atom like silver
does in the second reaction with copper.
Page 6:
1. Explain why it is necessary that
whenever reduction occurs, oxidation
must also occur.
Reduction occurs when electrons are
transferred from on atom to another. It can
also occur when the probability of finding an
electron near a particular atom shifts
directions in a covalent bond. In both cases
the electrons have to come from some
place, so at the same time one atom is
reduced, some other one must have been
oxidized, providing the electrons for the
reduction.
2. If one atom has higher
electronegativity than another atom what
is likely to happen when they bond
together?
(b) The atom with lower electronegativity
will take electrons from the other atom.
3. Observe the way the electrons get
redistributed in the reaction above.
Which element is reduced?
5. In a battery a redox reaction occurs in
which electrons are transferred
completely from one atom to another
through a wire instead of through direct
contact. Use the electronegativity table to
the right to choose a pair of metals that
you think would exchange electrons. Be
sure to describe which atom will be
reduced and which atom will be oxidized,
and explain your reasoning.
Because they all have different
electronegativities you could pick any pair of
metals to make a battery. The only
difference is which metal will be oxidized
and which one will be reduced. The one with
the higher electronegativity will be reduced
while the other one will be oxidized. For a
specific example take nickel and lithium.
Because lithium has a lower
electronegativity it will tend to give up
electrons (be oxidized) to nickel (or at least
nickel ions) which will become reduced.
Further Extensions