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Richard Feynman (See Gleik J, 1994) suggested that should
all scientific knowledge be destroyed and only one sentence
be available to pass on to the next generation - that
sentence should be:
‘That all things are made of atoms - little
particles that move around in perpetual motion
attracting one another when they are a little distance
apart, but repelling upon being squeezed into one
another.’ In this one sentence there is an enormous
amount of information about the world, if just a little
imagination and thinking are applied. (p358-9)
Of course there may well be other things you feel it
would be helpful or necessary to know if you were in the
process of trying to reconstruct the basic useful ideas of
science. Some of these, we hope, are explored in the science
knowledge units. However, the complete list should come
close to what you believe should be the science curriculum
for pupils in our schools. Download 1a provides a beginning
list of ‘other useful things to know about atoms and
particles' - there is plenty of room for additions (and
subtractions) but remember that there have to be good
reasons and evidence of both reasonableness and utility.
Above all on this planet atoms are (except in nuclear
reactions) indestructible and are constantly cycled by the
degradation of energy from the sun and from within the
earth.
Some views complementary to ‘constructivism’
Much of the science material currently covered on this
site takes an unashamedly constructivist view of learning -
there are, however, a number of valid and important
psychological insights and perspectives available from other
areas of learning/teaching theory that we sometimes tend to
undervalue. A useful, complementary (and provocative) view
of issues in research into the learning of chemistry is
given in Download 1b. This is a summary of the 1999
Chemistry Education Research Lecture given by Alex Johnstone
to the Royal Society of Chemistry. (Alex has researched and
written extensively about the teaching and learning of
chemistry and his publications are widely distributed in
appropriate journals.)
The paper (Download 1b) covers:
- A short critique of the emphasis, in science
education research, on pupils’ alternative
conceptions.
- Particular difficulties for chemistry learners (from
KS3 and especially beyond) caused by having to switch
attention rapidly between the macro-scale (What
is seen and experienced directly), the sub-micro-scale
(atoms, molecules, ions, electrons etc. that are
essentially invisible) and the representations (Symbols,
formulae and diagrams) chemists use in their writing
and explanations. There are issues also with
developing specialised vocabulary, but these are
similar in other subjects.
- Learners are essentially ‘information processors’
- and the system is prone to overloading and the
learner to ‘confusion’
- Specific chemistry issues are explored including the
mole, chemical equilibrium (learners usually come
first to an understanding of equilibrium in physics -
it seems that here lies the source of many of the
problems we have in thinking about the dynamic
process of chemical equilibrium in the face of the static
situation in physics.)
- Practical work in science is seen as leading to an
unstable information overload for the learner almost
by definition. This can be overcome by very careful
preparation and follow-up to practical sessions, but
in practice this is rare.
There are other specific ‘teacher behaviours’ that
can be employed to enhance learning (not evidenced here):
- Engagement and involvement of the learners.
- Mutual trust between teacher and student - and by
the ‘system’ in the teacher.
- Importance of ‘mastery learning’ of basic ideas
and skills so that ‘chunking’ can occur and so
reduce the demand on information processing. (e.g. For
a beginner a chemical formula such as H2SO4
acts as a number of separate bits of information
- two atoms of hydrogen, one of sulphur and four of
oxygen somehow joined together. With experience, use
and understanding this formula can carry with it the
chemistry of sulphuric acid as a single bit of
information.
- Importance of appropriate questioning and ‘wait
time’ for the students to answer. This is to
encourage thoughtful and considered answering rather
than guessing and rote learning. It can be extended by
using talk-partners to give pupils the time to
rehearse an answer before having to go public etc,
etc.
Download 2.1a: This is a power-point presentation from a
lecture on ‘Matter’ by Keith Ross. It is based on the
idea that when we throw something away we tend to think it
has ‘gone’. But matter cannot be destroyed, at least not
at an atomic level during normal chemical and biological
change. But to understand the fate of things thrown away we
need to know their chemical make-up, and how they might
interfere with (or help) living things. A study of recycling
is a wonderful starting point to help children understand
the structure of materials.
From a very early age we become familiar with the
presence of ‘things’ and ‘other people’ in our
environment and, well before we begin formal schooling, are
able to differentiate between ‘things’ and ‘living
things’ (Although it is a good while later that we begin
to accept plants and seeds as ‘living’ and later still
for bacteria and algae! What about viruses?)
Substances are the ‘stuff’ or ‘matter’ that all
things are made of. Initially we need to learn to
differentiate the things themselves from the substance(s) or
material(s) of which they are made. In fact most ‘things’
are made of many different substances so learning about this
is rarely complete and only sometimes important:
- Rivers, ponds, seas and lemonade are made mainly of
water
- Books are made of paper (paper is made mainly of
cellulose - an organic polymer - based on the element
carbon)
- Coins are made of metals (Almost always ‘alloys’
that are mixtures of different metallic elements.)
- Clothes are usually made from fabrics (woven from:
cotton threads, silk, wool, Terylene, nylon etc.
Sometimes the threads are made of mixtures of
different fibres. All these fibres are organic
polymers)
- Mountains are made of granite, limestone, dolomite,
sandstone (and many more rocks and soils - mostly made
of compounds of the element silicon)
Classification
It is often useful to classify substances into different
groups. All such classifications have their uses and
drawbacks. Download 2.1b is an analysis of some of the ways
we try to classify matter and some of the difficulties
associated with each of them.
These are often called the three states of matter
(Sometimes a fourth is added - the plasma state - but this
rarely of interest before A-level studies.). The problem of
using Solid/Liquid/Gas as a way of classifying materials -
since most are solids at room temperature - is discussed in
download 2.1b above.
Three key issues are:
- It is easy to distinguish between the three states
'solids maintain their own fixed
shape and volume; liquids have their own volume but
take the shape of their container and retain a level
surface. Gases take the shape of their container and
its volume since they tend to fill it. These are
fairly straightforward but the ideas need to be
practised and there are difficulties: e.g. finely
powdered solids seem to behave like liquids, they take
the shape of their container and can be poured - but the surface does
not remain horizontal when the container is tipped;
very viscous liquids flow very slowly and may seem
more like solids. A good way to distinguish between
powders (solids) and true liquids is to ask, “Can
they be piled up - will they stay in a pile?”
- Depending on the temperature most substances can
exist in all three states. The typical
example is water; at normal room temperatures it is a
liquid, below 0oC it freezes to become ice and at
100oC (and at normal atmospheric pressure) it boils to
become steam/water vapour. Actually water does slowly
evaporate at ALL temperatures if its surface is
exposed and the ‘air or space’ above the surface
is relatively dry - even frozen wet clothes will ‘dry’
on a washing line without the ice melting first. The
main exception to other substances melting and boiling
as the temperature rises is when they change
chemically before one or both of these happen, for
example wood.
- These states and changes in state are generally
called ‘physical changes’ and are usually modelled
or explained using the Kinetic Theory. (See
next section)
These will be found represented and explained in almost
every science or chemistry text-book written for pupils at
KS3 or above. It is instructive to see how well they make
sense to our teachers in training. It is not a trivial task to come to
an understanding of the nature of the particles involved in
any particular case - how the forces between the particles
and their size (and sometimes the shape) of the particles
affect their movement at particular temperatures and how the
conversions from solid to liquid (and reverse) and from
liquid to vapour (gas) and the reverse are controlled. (Note
that the freezing temperature and the melting temperature of
a substance are the same. It is also quite a sophisticated
task to distinguish between evaporation and boiling.)
Because the particles are able to move about in liquids and
gases - diffusion is possible and, if more than one type of
particle is present, the system becomes as mixed as
possible, with high concentrations of any particle tending
to spread out into places where the concentration is lower.
(Remember: even when the system is completely mixed the
particles continually move about - it is just there is no
overall change on a large scale.) It is interesting to note
that solid state diffusion occurs (very slowly) in metallic
substances, which is why annealing, for example, can change
the properties of a metal.
The particle model is identified a one of the key
scientific ideas in the KS3 strategy. Unit 7G of the KS3
schemes of work covers this topic.
See Download 2.3a for a discussion of two important
misconceptions concerning the particle representation of the
states of matter:
- Pupils (and text books) sometimes think particles
representing the liquid state are more spread out than
in solids - solids and liquids have similar densities
and they are virtually incompressible.
- they often think that particles representing the
gaseous state are moving with more energy than in the
liquid and the solid (this will be true only if the
gas is hotter than the liquid or solid).
Further misconceptions
- Pupils often think that there has to be ‘something’
(usually ‘air’) between the particles! Slide 20 of
Download 2.1a also shows a diagram drawn by post-GCSE
student to illustrate a ‘story’ of a water
molecule. This demonstrates a number of misconceptions
- especially how difficult it is to visualise the ‘nothing’
that is between the particles.
- Download 2.3b is the manuscript for a paper on
Science Graduates’ understanding of evaporation and
boiling which was later published in School Science
Review (Goodwin (2003)). This piece of research looks
at a more sophisticated level of understanding.
This classification often arises early in KS3 - and
sometimes at KS2 (with more able /interested pupils). It
introduces the various sorts of ‘particles’ that we may
be talking about and illustrates the changing meanings of
some of the important ‘particle’ words as we learn more
and are able to differentiate more as ideas develop.
The scientists’ views of ‘atoms’ has developed
hugely over the past 100 years - although the older view of
atoms at tiny indestructible spheres still serves for many
purposes. (In the simple kinetic theory the indestructible
sphere model also works for molecules - providing that no
chemical reactions occur.) During the first half of the 20th
century a model of the atom developed - with a very small
very dense nucleus (made of protons and neutrons) and
surrounded by a cloud of electrons. Most of the inside of
the atom is ‘empty space’ - it is the forces of
attraction between positively charged protons and negatively
charged electrons that make atoms seem to be hard particles.
The rearrangements of the electrons on the outer edges of
atoms - give rise to chemical ‘bonds’ by which atoms
sharing, transferring or letting electrons move relatively
freely become linked in various ways to form molecules,
ionic or metallic structures. Without exception these ‘bonds’
are formed by electrostatic attractions between oppositely
charged particles - arranged so that the overall structure
has the minimum energy. When these different substances
(chemicals) interact such that the bonding is rearranged we
have a chemical reaction and new substances are formed.
(Note: in real life it is not always obvious when new
substances are formed - this requires both careful
observation, tests and sometimes some ‘chemical intuition’).
A description of chemical bond formation will be found in
most science text-books at GCSE and above but they
frequently give ‘rules’ based on ‘octets’ of
electrons without much mention of electrostatic attraction
(except between oppositely charged ions) or the system
having to find an energy minimum within which to ‘rest’
if it is to be stable.
A significant resource, produced by Keith Taber and
published by the Royal Society of Chemistry (Taber - 2002)
explores many of the misconceptions experienced in the
learning of chemistry. Copies were distributed to all
secondary schools when the materials were published, should
be available in libraries and are still available from RSC.).
Trainee teachers who will be covering the chemistry
curriculum at GCSE and above really should have access to
this very important research, much of which is freely
available on line:
(summary of resources)
http://www.uoi.gr/cerp/2001_February/07.html
(full text available as PDF)
Keith Taber’s worksheets to use with pupils
can be downloaded from: http://www.chemsoc.org/networks/learnnet/miscon2.htm
There are only about 100 different sorts of atoms (a
version of the Periodic Table of Elements is shown in Slide
13 of Download 2.1a) A much more sophisticated version is
available at (http://www.chemsoc.org/viselements/
). An element is a substance that is made up of only one
kind of atom. (It is possible for the number of neutrons in
the nucleus to vary, within limits. This allows for atoms of
the same element to exist with slightly different atomic
masses. These are called isotopes and the measured relative
atomic mass (RAM) of an element is the weighted average of
the isotopes present. For this reason the RAMs of most of
the elements are not whole numbers.) It is the number of
protons in the nucleus (and hence the number of electrons in
the neutral atom) that determines the actual element and
defines the Atomic Number.
When atoms of one element join together with atoms of one
or more other elements the result is a chemical compound.
The energy requirements usually require that atoms have only
one or a limited number of ways in which they combine and
these compounds can be represented by a definite chemical
formula.
Even the smallest ‘bit’ of a substance that it is
possible to see contains a huge number of atoms (and often
molecules) - in every day language we may talk about a drop
of water in a spray with a volume of .000000001cm3
(equivalent to a diameter of around .001mm - almost
invisible without a microscope) as a particle. This would
however, contain well over ten million million molecules of
water! So the particles in our model really are very small.
(See also Download 2.3a).
Different substances - especially gases, liquids and
powdered solids - can often be mixed together in almost any
proportions. Provided that no chemical reactions occur -
these remain as mixtures.
A fairly full picture of expectations can be found in the
Science National Curriculum -
- Pre-school children should develop language to
describe and name a variety of living and non-living
things and begin to recognise some common substances.
They should begin to realise the difference between an object
(eg a ball) and the substance it is made from (eg
rubber)
- KS1 some meaningful play and experience with solids
liquids (and gases). Ideas of conservation of material
during ordinary processes will be developing but most
will be quite happy that the water simply ‘disappears’
when puddles evaporate and candles ‘disappear’ when
they burn; also that crushing a solid to form a powder
or pressing a lump of plasticene into a flat shape may
decrease their weights. They may appreciate some
reversible changes such as ice melting and water
freezing but may not realise that water and ice are the
same substance. They will develop some specialised
language relating to common processes involving
materials such as cooking food, weather, shopping,
vehicles, washing etc..
- At KS2 classifications of the states of matter should
be becoming firmer and they should recognise that
heating and cooling can cause reversible changes -
whereas other changes are more permanent. An
understanding of the water cycle will develop. The idea
that water can exist as a gas, indeed that air is a gas
and has weight are difficult concepts, and many pupils
will reach GCSE still unclear about the massive nature
of gases (see download 3). Some substances can be
separated from each other by physical processes. Very
early beginnings of particle ideas - scale is unlikely
to be appreciated - but many children will begin to pick
up some of these ideas from TV, books, parents and
peers, even if they are not emphasised at school.
- KS3. Continuing development of ideas and experiences
with materials - their properties, uses, changes with
temperature and pressure, changes of state, chemical
changes. Development of more systematic explanations
in terms of particles and increase of movement energy
at temperature increases. Qualitative understanding of
melting, freezing, diffusion, evaporation,
condensation, expansion. Gases have mass - an idea
that needs to be developed carefully. Ideas of atoms,
ions, molecules and metals. Trends in the Periodic
Table of Elements. Atomic structure and radioactivity.
It is at this stage that pupils must begin to
appreciate the difference between matter at an atomic
level (indestructible particles that change their
arrangements but retain their identity) and matter
at a bulk level (where things change, and matter
seems to come and go). See Download 1b (Alex
Johnstone 1999) again.
- KS4 Here the idea becomes established of an element
(with its own particular unchanging atom) their
arrangement in the periodic table and the way their
electronic structure helps to explain the sort of
bonds they can make and the relationship between the
types of bonding in materials and their physical
properties and applications. Some pupils will become
familiar with the mole concept.
- Gleik J (1994) ‘Genius - Richard Feynman and
modern physics’, London, Abacus.
- Goodwin A (2003) ‘Evaporation and Boiling - trainee
science teachers’ understandings.’ School Science
Review, 84 (309) pp 131-141.
- Littledyke, M. Ross, K.A. and Lakin L. (2000) Science
Knowledge and the Environment A guide for Students and
Teachers in Primary Education. London David Fulton.
- Ross, K.A. (1997) ‘Many Substances but only five
structures’ School Science Review, Vol 78 no 284
pp79-87
- Ross, Lakin and Callaghan (2004) ‘Teaching
Secondary Science’ Second Edition London: David
Fulton
- Taber K (2002) ‘Chemical misconceptions -
prevention, diagnosis and cure. Volume 1: Theoretical
Background. Volume 2: Classroom Resources.
Downloads in this Unit:
Section Developed by:
Alan Goodwin (MMU) with additional material by Keith Ross
(UoG)
May 2006
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