Chemistry
Topic 2 Atoms and elements
Improving practical work
Introduction
This topic does not lend itself easily to laboratory practical work. This is because it is not possible
to observe atoms directly. The concept of atoms is abstract – it is a model used to explain
observations. However, by providing practical activities in which students observe chemical and
physical changes, you can encourage them to think about the changes that occur at the particle
level and provide opportunities for them to use their new level of understanding when discussing
laboratory chemistry.
The practical detailed here will give students such an opportunity by guiding them through a simple
physical change, leading to an explanation of what happens at the particle level during a chemical
reaction.
The use of atomic models, either pre-purchased or created using modelling dough and cocktail
sticks, will increase engagement and allow the abstract ideas presented here to become concrete.
If students are first allowed to create 3D models, they will find it easier to visualise the atomic
make-up of a substance and later to represent it on paper.
A few ideas for some classic practical activities
 Investigating samples and molecular make-up
Prepare samples of a range of elements for students to look at – create accompanying atomic
models or prepare atomic diagrams so they can begin to link names to molecular make-up. A good
representative set of samples and models would be hydrogen (H2), oxygen (O2) and chlorine (Cl2);
a range of metals with images of the solid particle diagram (molecular modelling kits are not
appropriate for metals as they cannot show the nature of the metallic bond); and coal, where the
accompanying atomic model is a single black atom of carbon.
 Investigating elements reacting with water
Students can investigate elements and their reactions with water and air – the rusting of iron and
the conditions required for this to take place is a straightforward investigation which highlights
planning a fair test and the relative speed of chemical changes. Three tests tubes can be prepared
into which an iron nail is placed: air (in which the iron will rust, owing to the moisture in the air);
boiled water with a layer of oil (boiling eliminates oxygen from the water and the oil keeps the
oxygen away from the nail, which therefore will not rust); and air with calcium chloride and a bung
(CaCl2 is a drying agent which eliminates the water and so prevents rusting). These can be left for
a week and then viewed again, or ask the technicians to prepare a set in advance so you can
show the one made earlier, stressing the time it took for the reactions to occur.
 Investigating the properties of elements
Students can investigate the properties of elements, defining them as metal and non-metal or
grouping them according to their states at room temperature. They can also group them according
to other easily tested properties. An engaging way to do this is to present groups of students with
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Chemistry • Topic 2 • Atoms and elements
some labelled samples for which they are to create an identification key, together with suitable
apparatus for carrying out tests on their samples. Also provide each group with a second set of the
same samples marked with letters only. Once the keys have been prepared, take in the labelled
samples. Groups then swap samples, testing equipment and keys, and identify the unlabelled
samples.
A good set of examples would be:
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iron (magnetic)
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copper (will conduct electricity but not magnetic)
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calcium (will not conduct but will react with water)
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carbon powder (will not conduct and will not react with water).
You would need to provide ways of testing conduction of electricity, reaction with water and
magnetic properties.
A second set could be:
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zinc (solid and reacts with acid)
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carbon powder (solid but won’t react with acid)
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oxygen gas sealed in a test tube (a gas and will re-light a glowing splint)
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carbon dioxide, again sealed in a test tube (can be air – a gas and won’t re-light a glowing
splint).
You would need to provide 1 M HCl, glassware, a lit Bunsen and splints. Students may need to be
prompted to make the first classification of solid or gas.
 Teacher demonstrations
Iron and sulfur
Comparisons of elements and the compounds they form is an engaging and often awe-inspiring
activity. The classic teacher demonstration of iron reacting with sulfur allows a comparison of the
properties of the reactants, iron and sulfur, and the properties of the compound, iron sulfide.
Properties that can be compared include colour, magnetic properties and density. For instructions,
follow this link to the Nuffield Foundation website and search for ‘iron and sulfur reaction’:
www.nuffieldfoundation.org/
This idea can be extended to class activities comparing other elements and compounds:
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water with samples of hydrogen and oxygen
a copper sulfate crystal with samples of copper, sulfur and oxygen
calcium carbonate with samples of calcium metal, carbon and oxygen.
Sodium and chlorine
Another excellent teacher demonstration is the reaction of sodium metal with chlorine gas to make
sodium chloride. Again, for instructions, follow the link above to the Nuffield Foundation website
and search for ‘heating Group 1 metals in air and chlorine’.
This is a visually spectacular experiment and students’ familiarity with the properties of the product
(table salt) can enhance their engagement with the properties of the reactants, especially the toxic
nature of chlorine.
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Chemistry • Topic 2 • Atoms and elements
Practical work in everyday teaching
Here are a few ideas to help you incorporate skills building for practical work into your everyday
lessons on this topic.
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Always show students samples of any elements you make reference to. This helps to keep an
abstract idea rooted in the concrete, observable arena.
Make use of practical starter activities, such as providing a sample of an element and asking
students to investigate a specified property: ‘does your sample float on water?’ or ‘is your
sample magnetic?’ Have a set of testing equipment available every lesson including ice
cream tubs to fill with water, a set of magnets, a power pack and wires with a bulb to test
electrical conductivity and nails to test hardness. Students can then develop the skill of
selecting equipment to investigate properties of materials. Some good examples which work
well include copper, iron, aluminium foil, graphite (carbon) and sulfur.
Offer a model for measuring the mass of atoms. You can use finding the mass of a grain of
sand as an analogy for how scientists could find the mass of an atom. Show students that one
grain of sand does not register on an electronic balance. Give them a tub of sand and ask
them to plan how they could determine the mass of a single grain of sand. They should
present a results table, with headings and units, and the calculation required. Students will
quickly arrive at the idea of measuring a sample and dividing the mass by the number of sand
grains – however, the trick is to have a sample small enough so they do not need to count out
thousands of sand grains but large enough to register on the balance. The results table should
include – mass, number of grains of sand and the calculation mass/number of grains. They
should include five different sample sizes to identify a trend (in this case a linear relationship)
and three repeats to ensure reliability. If time allows, a graph could be drawn where the
gradient of the (hopefully straight) line will be the mass of one grain of sand.
Activity: Investigating atoms
Follow this link to a video of this practical activity: Video: Investigating atoms.
The aim is to allow students to make links between observation and particle theory ideas, and
begin to write word equations using state symbols.
The worksheet for the practical activity gives directions for three simple experiments: melting,
dissolving and a chemical reaction. Each one is performed quickly by students in pairs at their
bench. There should be adequate time for all three in a lesson. If other activities also need to be
completed, students could complete the experiments, record their observations and develop their
explanations for homework. The questions progress in terms of complexity of concepts and the
demand of the particle diagrams. Depending on the placement of the topic you may need to recap
how to represent solutions and diatomic elements, and how to draw substances made of different
atoms. The activity will work equally well if these ideas have yet to be studied, but the level of
detail expected in the particle diagrams will need to be adjusted.
Follow this link for the student worksheet: Activity: Investigating atoms.
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Chemistry • Topic 2 • Atoms and elements
 Answers to the activity
Experiment 1
This is a change of state. Students should choose a representation of the solid wax and show a
solid formation change to liquid and back to solid. All particles should be drawn to be identical
throughout.
Experiment 2
Experiment 2 is dissolving. Students should represent water as a liquid and sodium chloride as a
solid (depending on approach and timing of this activity, students may represent sodium and
chlorine as two different atoms or as one – either is fine if appropriate for the class). The final box
must show both water and dissolved sodium chloride – based on the note above, if they show
sodium chloride as two atoms, these must then be separated in the solution; if they have not made
this distinction for compounds then the same representation, but spread through the water, is
acceptable.
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Chemistry • Topic 2 • Atoms and elements
Experiment 3
This is a chemical change. Magnesium should be represented as a solid and hydrochloric acid as
a solution – liquid formation showing water and hydrochloric acid (the representation of the acid
will depend on placement of this topic before or after understanding acids as solutions. Judge the
expected level of detail for your class.) The products show hydrogen as a gas (diatomic if this idea
has been covered) and magnesium chloride solution.
 Hazard assessment
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Safety glasses needed for 1 M acid
Usual laboratory safety around heating – standing, hair tied back and procedure if burnt
 Technician notes
Equipment needed
Each pair of students will need:
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A sample of solid steric acid set up in a boiling tube
Bunsen burner, mat
Boiling tube holder
Measuring cylinder
Boiling tube and boiling tube rack
Spatula
Sodium chloride solid
1 M HCl
Mg pieces
Procedure
The procedure is described on the student worksheet.
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