Introduction to Atoms and
the Nature of Science
Suggested
Year Group:
3-4
Relevant KS2 Links: SC1 1b, 2a, 2d, 2j, 2k, 2l; SC3 2a, 2d
Plus basic foundation for: material properties; electricity & magnetism; solids,
liquids & gases; DNA as the basis of life and others.
Base Concepts Conveyed: Good scientific theories must make testable
predictions. Materials are composed of collections of extremely small
objects called “atoms.”
EQUIPMENT
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About 30 tarnished 1p coins (one for each student in the class);
A dozen steel nails (about 3 or 4 cm in length);
Two clear cups or jars (large enough for the nails);
A small bottle of distilled white vinegar;
Some table salt;
A spoon;
A cloth;
Some water
INTRODUCTION:
This lesson serves several purposes. It introduces students to the concept of atoms as the
constituents of all the materials we see around us and demonstrates how this notion can be
tested in a very visual and interesting way. It touches on what it means to dissolve
something and that things don’t just disappear. It is also used as a springboard to more
generally explore the nature of science, what makes a good scientific theory and details of
how to use the scientific method to clearly test predictions, which is the key to scientific
thinking.
(modified from Exploratorium activity: http://www.exploratorium.edu/science_explorer/copper_caper.html )
TEACHING:
Begin by discussing with the class the nature of science, what a ‘theory’ is and ask how
they think something is judged to be a good scientific theory. Most (including adults!) get
this wrong and will say that a good scientific theory is judged based on what it can
explain. Ask if they think this is correct. In fact, it is not: a good theory is judged based on
what it can predict. In fact, a pretty good definition of “science” is that it is the approach
that leads to the most accurate and reproducible predictions. As an example, you could
propose that magic, invisible genies race around making everything happen and keep
tricking us into thinking something else is going on. That is a theory that can be used to
“explain” everything, but it isn’t science because it lacks the ability to make any clear
predictions, since the genies can do anything. Prediction is the thing that makes science
so practical and useful.
What is a
scientific
theory?
At the end of this discussion, reward each of the students for doing such a good job by
giving them a 1p coin (there are limits to a teacher’s generosity!). Have them hold up their
coin and ask if they know what it’s made from. They will probably say copper. In fact,
since 1992, UK 1p and 2p coins have been made with a steel core and a copper coating.
Prior to that they were, indeed, mostly copper (you can see this using a magnet). But do
they know where copper and other metals come from? Some may say from underground,
which is great, this is certainly where it is found… but where was the metal itself actually
made? The surprising answer is that all metals were made in the middle of enormous,
exploding stars (supernovae) that happened somewhere in the galaxy before the earth was
formed. So, each of them is now basically holding a piece of an exploded star!
Now ask them to imagine they were able to break the coin in half. Imagine they could
keep doing this, making smaller and smaller pieces. Could they keep doing this forever?
What is the smallest piece of metal they could ever have? Some may know that this is
called an atom. In fact, “atom” comes from the Greek wording meaning “something that
cannot be further divided.” There are lots of different kinds of atoms. Combinations of
atoms that are held tightly together are called “molecules.” Everything around us is made
of atoms and molecules. Tell the students that they probably know about one of these
molecules: have they heard another name for water that starts with “H” ? H2O means two
atoms of Hydrogen and one atom of Oxygen.
But you can’t see the individual atoms because they’re very, very, very small. To get an
idea of how small, ask the students to guess how many atoms are in the 1p coin. The
astonishing answer is about 30 thousand million million million! So they are much
smaller than you’d ever be able to see, even with a magnifying lens. If that’s the case,
how can you show that there are such things as atoms? Instead of trying to look at just one
atom, we could try to move enough atoms around so we can see their effects.
Ask the students to look at their coins again and notice that they’re a bit dull and
tarnished. This is because the atoms of copper on the outside of the coin can combine with
some oxygen atoms from the air to make a molecule called copper oxide, which is a kind
of rust. These are the atoms we will move around. Have a volunteer come help you to
pour vinegar into each of the two cups, filling each up about a third of the way. Into each
cup, ask your volunteer to now add about a teaspoon of salt and stir until dissolved. Put
one of these cups aside. Explain that the cups now have atoms in them that like to attach
to the copper oxide rust in a way that pulls it apart and takes those atoms off the coin. To
show this, ask your volunteer to drop their coin in the cup you still have and to describe to
the class what happens. They will see the coin almost instantly turn shiny! Now take that
same cup around to the rest of the class and let them each drop their coins in to see the
dramatic change. Remove the coins (but hang onto the cup!), put them on the cloth and set
them aside. Note: rinse the coins off if you are not going to do the additional section at
the end, otherwise leave them as they are.
Ask the students, “Where has the copper that was in that rust gone?” If they say these
are now in the cup, note that they are excellent scientists because they have made a
prediction. It could have been explained as being the result of the invisible genies casting
a “clean-up” spell and that the rust simply disappeared, but that wouldn’t lead to any
prediction about what’s in the cup now. Ask someone to look in the cup to see if there are
any copper atoms floating around. Of course, they can’t see any because copper atoms as
so small. Then how can we tell that there are really copper atoms in the cup and that this
isn’t just another fairy story? Perhaps we can put the atoms onto something else to make
them easier to see: have another volunteer come up and hold the cup. Ask them to take a
good look at the steel nails and then drop half of them in the cup. Explain that some of the
Where
does metal
come from?
What is the
smallest
piece of
metal you
can have?
How many
atoms are in
a 1p coin?
Why do
copper coins
tarnish?
Where have
the copper
atoms gone?
copper atoms in the cup can swap places with some of the iron atoms in the steel. Ask
your volunteer to keep looking to see if they notice anything. This reaction is a little bit
slower, but after about 30 seconds, you should notice that the nails in the cup now look
darker. When the change seems pretty clear, take the nails out, rinse them off , pat them
dry and then show them around side-by-side with the nails which were not put in the cup.
The darker coating is due to copper atoms that have plated out onto the nail. So you have,
indeed moved copper atoms from one thing to another!
But hang on, how do you really know that’s true? What if the nails just changed colour
from interacting with the vinegar and salt so that copper atoms had nothing to do with it?
How can you tell that the vinegar and salt alone didn’t do this? Discuss this with the class.
Lead them to realise that you have another cup with vinegar and salt that never had any
copper in it. How does that help? Put half of the remaining steel nails not previously used
into this cup. What does the class think will happen? Excellent! The two theories lead to
different predictions: if copper atoms are responsible, the nails will remain unchanged. If
just vinegar and salt were responsible, they will get darker just like before. Again, this is
thinking like a real scientist.
While your volunteer keeps looking in the cup to see if anything is happening, explain
that scientists would also call this other cup “the control,” which is where you do the
experiment in exactly the same way, except for the one thing whose effect you wish to
study (in this case the copper coins), so you can be sure that you’ve not been fooled by
something else. Remove the nails from the cup now, rinse them off and compare them
with the two groups of nails from before. The nails have not gotten any darker and look
like the ones that were not put in anything. So, it really must have to do with atoms from
the coins that were moved to the nails!
But there’s a surprise ending in store: remember that you dissolved table salt in the
vinegar? Table salt is made of the atoms sodium and chlorine. What does it mean to
dissolve something? The atoms get separated and mixed around in the liquid. Take a look
again at the coins that you set aside and hand these back to the students. They now have
patches of a green coating on them. Some of the chlorine atoms from the salt have
combined with oxygen atoms from the air and the copper atoms on the surface of the coin
to form a mineral called malachite. So, not only have you moved some copper atoms from
the coins to the nails, but you have also moved some atoms of chlorine from the salt to the
coins!
ACTIVITY:
Have the students go to their seats with their coins. Ask the students to do the associated
worksheet where they try to picture how the atoms were moved around and remember
what predictions were tested. For extra activities, they could research other combinations
of atoms and make a fact sheet.
How do you
know it was
really the
copper atoms
that moved?
What is a
“control?”
What does it
mean to
“dissolve”
salt?
Quick Reference
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Explain definition of scientific theory (based on prediction, not just explanation).
Examine 1p coin, talk about where copper comes from and how it’s made.
Define “atom” and relate to breaking coin into smaller and smaller pieces.
Talk about the size of atoms (30 thousand million million million in a 1p coin).
Define “molecule” as combination of specific number of atoms held together (e.g. H2O).
Explain tarnish on coins as rust from combination of oxygen and copper (copper oxide).
Immerse coins in solution of salt & vinegar. What happens?
Where have the atoms from the rust gone? Prediction: must be in solution.
Drop nails in cup and examine after ~30 seconds. What has happened?
How do we know darker colour is from copper atoms?
Introduce idea of “control” cup of salt & vinegar that hasn’t had coins inside.
Compare nails from both solutions to show atoms from coins are responsible.
Look at coins previously removed. Why are they green?
Talk about salt being made from atoms of sodium and chlorine.
What does it mean to dissolve something?
Talk about atoms/molecules being separating and mixed in liquid.
Explain how chlorine atoms can mix with oxygen and copper to make malachite.
Moving Atoms
Describe how copper atoms were moved around in the
experiment and draw a picture of what this might look like
if you could look VERY closely at the coins and the nails.
Use arrows to show how the atoms moved.
What was different about the two cups of liquid that
were used?
How were these cups used to show that it really was
copper atoms that made the nails get dark?