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7 Elements, compounds

and mixtures
There are millions of different
substances in the world. Some,
like water, occur naturally. Others,

like paper and plastic, are made

in factories. Some substances,
like sugar and blood, are made by
living things. All substances have
one important thing in common:
they are all made of the tiny
building blocks of matter that
wecall atoms.

Think about substances

How did plumbers get their name?
Which metal can drive you crazy?
Can water be split?
Can you breathe nitrogen gas?
What is most of an atom made up of?
Just what is plastic made from?
Which precious gem is made from the
same substance as charcoal and soot?

In this chapter:
Its elementary 228
7.2 Elements: The inside story 230
7.3 Compounding the situation 233
7.4 Grouping elements 236
7.5 Patterns, order and organisation:
Chemical name tags 238
7.6 Making molecules 240
7.7 Carbon: Its everywhere 242
7.8 Thinking tools: Affinity diagrams and
cluster maps
Study checklist/Digital resources 244
Looking back 245
ICT Activity

Science TV 247
How small are the bits that matter?

INVESTIGATION 7.1 How small are the bits?

AIM To investigate Number Length of strip

division of matter ofcuts (approximate)
0 30 cm
1 15 cm

2 7.5 cm (easy?)

6 The first three cuts along the strip of paper
8 1 mm (youre doing well

to get this far!)
Continue this process until you can no longer cut
10 the strip in half.
1 How many cuts were you able to make? Was it
18 1 micron (1millionth of more or less than your prediction?
a metre, onethousandth
2 Estimate the number of cuts you would
of a millimetre)
need to make before the strip would be too
22 small to see.
31 The size of a single atom

Whats inside?
How do you know whats inside a substance when you cant actually
see inside it and it is so small that you cant see it even with the most
powerful microscope? It seems impossible but it can be done!


AIM To experience the difficulties of describing an

object that cannot be seen 1




7 Elements, compounds and mixtures 227


Its elementary
Lavoisier and hydrogen
Watch a video from The story of science about the discovery of the
About 1000 years ago, when kings and queens lived  eles-1772
in castles and were defended by knights
in shining armour, there lived
the alchemists. knowledge passed down by these
people, the world as we know
They chanted secret spells while it would be very different!
Twelve important substances

they mixed magic potions in their

flasks and melted metals in their were discovered during these
furnaces. They tried to change ancient times: gold, iron, silver,
ordinary metals into gold. sulfur, carbon, lead, mercury,
They also tried to find a potion tin, arsenic, bismuth, antimony
that would make humans and copper. Alchemists discovered
live forever. They studied the five of these.
movements of the stars and claimed to be able to
see into the future. Kings and queens took the advice
of the alchemists veryseriously. Real science
The alchemists never found the secrets they were In about the seventeenth century, people stopped
looking for, but they did discover many things thinking about magic and instead carried out
about substances around us. During the investigations based on careful observations.
same period people who worked These new seekers of knowledge
with materials also helped us to were called scientists. They
understand many everyday discovered that the 12
substances. Blacksmiths worked substances could not be broken
with metals to make stronger down into other substances.
and lighter swords and Scientists investigated many
armour, fabric dyers learned common everyday substances
how to colour cloth, and potters as well, including salt, air,
decorated their work with glazes rocks, water and even urine!
from the Earth. Without the They discovered that nearly


Lewis Carrolls Mad Hatter character in

Alices Adventures in Wonderland was
mad because mercury was used in the
making of hats.

228 Science Quest 8

everything around us could be broken down into sodium, potassium and mercury need special care and
other substances. They gave the name element to handling. Sodium and potassium are soft metals that
the substances that could not be broken down into can be cut with a knife. They both get very hot if they
other substances. Between 1557 and 1925, another come into contact with water. They are stored under
76 elements were discovered. We now know that oil so that water in the atmosphere cannot reach them.
92elements exist naturally. In recent years scientists
working in laboratories have been able to make at least Elements are rare
another 24 artificial elements.
Most of the substances around you are made up of two
or more elements. You will not be able to find many
Warning! Danger! of the 92 naturally occurring elements in their pure

Many elements are safe to handle. However, there are form. It is possible, however, to examine many of the
also many that are not. For example, the elements elements in the school laboratory.


Checking out appearances 1

AIM To examine and describe the properties of

aselection of elements

Elements State Description In which substances might the element be present?

Hydrogen Gas Clear, colourless, explosive Acids, water





8 work
sheet 7.1 How big is an atom?

7 Elements, compounds and mixtures


Elements: The inside story

About 2500 years ago a teacher named Democritus Rutherfords
model of the atom
lived in ancient Greece. He walked around the gardens
with his students, talking about all sorts of ideas. Positive nucleus

Democritus suggested that

everything in the world
was made up of tiny

particles so small that they

couldnt be seen. He called Electron
these particles atomos,
which means unable to
be divided. Other thinkers In 1911, New Zealander Sir Ernest Rutherford used
at the time disagreed with some of the new discoveries and inventions to prove
Democritus. It took about that atoms were not solid particles.
2400 years for evidence He fired extremely tiny particles at a very thin sheet
of the existence of these of gold. Most of the particles went straight through.
atoms (as we nowcall Only sometimes did they bounce off as if they had hit
them) to be found. something solid. He concluded that the tiny particles
could be getting through only if most of each atom
Atoms and elements consisted of empty space.
Niels Bohr proposed the next model of the atom.
We now know that each element is made of its own
He suggested that the electrons changed their orbits
particular kind of atom. Gold contains only gold atoms, around the positively charged nucleus and formed
oxygen contains only oxygen atoms, carbon contains only electron clouds.
carbon atoms and so on. But what is it that makes atoms
different from one another? To answer this question we Orbital electrons Nucleus, containing
need to know a little bit more about the atom. negatively charged positively charged protons
For scientists, the atom was like the mystery box
on page 227. Even though the atom couldnt be
seen, scientists did experiments over many years
and they thought carefully about the information
they gathered.
Bohrs model of the atom
Finding evidence for the existence of atoms was
not possible until Galileo wrote about the need
for controlled experiments and the importance of
accurate observations and mathematical analysis in
the 16th century. Galileos scientific method, along
with the development of more accurate weighing
machines, was used by John Dalton in 1803 to show In 1932
that matter was made up of atoms. He proposed that James Chadwick
atoms could not be divided into smaller particles and found another
that atoms of different elements had different masses. type of particle
For the next 100 years, scientists thought the in the nucleus
atom was a solid sphere, but discoveries including of the atom
radioactivity and electric current, and new technology the neutron.
such as the vacuum tube and Geiger counters, allowed
scientists to peek inside. The ChadwickBohr model

230 Science Quest 8

Inside the atom
It is now understood that all atoms are made up of
small particles.
The amount of negative charge carried by each
electron is the same as the amount of positive charge
carried by each proton. In an atom, the number of
protons is equal to the number of electrons, so there is
no overall electric charge.

Moving very rapidly The particles in the

around the nucleus are centre of an atom are called Helium atoms are lighter than all others except

electrons. Electrons protons and neutrons. hydrogen atoms. This blimp is filled with helium.
are much smaller in size and Together they form the
weight than both protons and nucleus. Each proton
neutrons. Each electron carries a positive
carries a negative electric charge. Neutrons Atomic numbers
electric charge. have no electric charge.
The number of protons in an atom is called its atomic
number. Each element has a different atomic number.
The blimp above is filled with helium, which has an
atomic number of 2. Helium atoms are lighter than all
others except hydrogen atoms. All carbon atoms have
six protons inside the nucleus, so the atomic number
of carbon is 6. For each proton in the carbon atom it
also has one electron, meaning a carbon atom has six
electrons. Carbon atoms can have 6, 7 or 8 neutrons in
their nuclei. The lightest element is hydrogen, which
has one proton in each atom and an atomic number
of 1. The heaviest natural element is uranium with 92
protons in each atom.

Modelling an atom
AIM To model an atom and observe what makes up most DISCUSS AND EXPLAIN
of an atom


7 Elements, compounds and mixtures

Whats in a name? For example:
Na = sodium (natrium)
As the early scientists discovered more and more Pb = lead (plumbum)
elements, it became more important that they all Hg = mercury (hydro argyros)
agreed on what to call them. Each element was given a Ag = silver (argentum)
name and a chemical symbol. K = potassium (kalium)
The chemical symbols of most elements are very easy to Fe = iron (ferrum).
understand. The symbol sometimes starts with the capital The names and symbols of some of the elements
letter that is the first letter of the elements name. For some have some interesting origins.
elements that is the complete symbol. For example: Einsteinium (Es) is named after the famous scientist
O = oxygen, C = carbon, Albert Einstein.

N = nitrogen, H = hydrogen. Polonium (Po) was discovered by another famous

scientist, Marie Curie. She named polonium after
When there is more than one element starting with Poland, the country of her birth.
the same capital letter, a small letter is also used. Helium (He) was first discovered in the sun. It is
For example: named after Helios, the Greek god of the sun.
Sodium (Na) was first called by the Latin
Cl = chlorine, Ca = calcium,
name natrium.
Cr = chromium, Cu = copper.
Lead (Pb) also used to have a Latin name, plumbum.
If an element has a symbol that doesnt match its Thats where the word plumber comes from. The
modern name, thats because the symbol is taken from ancient Romans, who spoke Latin, used lead metal
the original Greek or Latin name. to make their water pipes.


4 16



9 18


11 19

232 Science Quest 8


Compounding the situation

There are millions and millions of different substances in the
world. They include the paper of this book, the ink in the print,
A compound is completely different from
the air in the room, the glass in the windows, the wool of the elements of which it is made. Pure
your jumper, the cotton and polyester in your shirt or dress, salt consists of the elements sodium
the wood of your desk, the paint on the walls, the plasticof and chlorine. Table salt is a mixture that
your pen, the hair on your head, the water in the taps and consists mainly of pure salt.

the metal of thechair legs. The list could go on and on.

All substances can be placed into one of three groups: When the atoms of
elements, compounds or mixtures. different elements bond
Elements are substances that contain only one type together, a compound
of atom. Very few substances exist as elements. is formed. When heated
Most substances around us are either compounds together, the elements
or mixtures. iron and sulfur form a
Compounds are usually very different from the new compound called
elements of which they are made. In compounds, iron sulfide. Iron sulfide
the atoms of one element are bonded very tightly has the formula FeS. Every compound has a formula
to the atoms of another element or elements. comprising the symbols of the elements that make it
The elements that make up a compound are up. Unlike mixtures, the elements within a compound
completely different substances from the cannot easily be separated from each other.
compound. For example, pure salt (sodium Elements can be separated from compounds in
chloride) is a compound made up of the elements several ways. These include:
sodium (asilvery metal) and chlorine (agreen, passing electricity through a compound
poisonous gas). burning the compound
Mixtures can be made up of two or more elements, mixing the compound with other chemicals.
two or more compounds or a combination of Each of these methods involves a chemical reaction
elements and compounds. The substances that in which completely different substances are formed.
make up mixtures can usually be easily separated
from each other. When the parts of a mixture are
separated, no new substances are formed. Fizzy soft WHAT DOES IT MEAN?
drink is a good example of a mixture. It contains
water, gas, sugar and flavours. If you shake the soft
drink, the gas bubbles separate from the water and
go into the air. You
still have the water in
Some common substances
the bottle and the gas
in the air; they are just Substance Type Composed of: Scientific name
not mixed together Gold Element Gold Gold
any more. The parts
of the mixture can be Diamond Element Carbon Carbon
separated quite easily. Water Compound Hydrogen and oxygen Dihydrogen oxide
The gas escapes when
Pure salt Compound Sodium and chlorine Sodium chloride
the lid of the container
is opened, and the Brass Mixture Copper and zinc Brass
water can be separated Soft drink Mixture Water, sugar, carbon dioxide and other
by evaporation, leaving compounds
behind sugar and
Sea water Mixture Water, sodium chloride and other compounds
some other substances.

7 Elements, compounds and mixtures 233

Splitting water INVESTIGATION 7.6
We are surrounded by water. It is in our taps, in
our bodies, in the rivers, in the sea, in the air and it Making a compound from its elements
comes down as rain. We wash in it, cook with it and AIM To use a chemical reaction to make a compound
drink it. We cannot live without water. Water is not from its elements
an element it can be broken down into simpler
substances. The illustration below shows an apparatus
called a Hofmann voltameter. Water is placed in
the voltameter, which is connected to a battery. The
electricity splits the water into the elements of which it
is made: hydrogen and oxygen.

Hydrogen and oxygen are both elements. They METHOD AND RESULTS
are both gases, and they look the same; they have
no colour and no smell. Oxygen is necessary for
substances to burn even hydrogen does not
burn without it. Hydrogen is a much less dense gas
than oxygen. This means that a balloon filled with
hydrogen will float up very high, but one filled with
oxygen will not.
The element hydrogen is present in almost all acids.
By placing a piece of metal in an acid, the hydrogen is
forced out. The hydrogen can be collected and tested
with a flame.
The element oxygen is present in water, air, rocks 1
and even hair bleach. Oxygen is the gas that all living
things need to stay alive. It is also necessary for all
substances to burn. When hydrogen gas is burned, 2
it combines with oxygen in the air to form water.
This releases a lot of energy. If large amounts of 3
hydrogen and oxygen are used,
enough energy can be 4
released tolift a
space rocket. Oxygen

Hydrogen 6


Water is split in a Magnesium

Hofmann voltameter. ribbon inside
Theclear gas in the
left tube is hydrogen.
The gas in the right Pipeclay triangle
tube is oxygen. Bunsen
What do you notice burner
about the amounts of Tripod
hydrogen and oxygen
that are produced?

6V battery
or power supply

234 Science Quest 8

Lets collect an element
AIM To observe a chemical reaction between a metal
and an acid

Collect the hydrogen gas

by placing the second test
tube over the first.



Dilute hydrochloric acid

Piece of magnesium metal






sheet 7.3 Pure substances

7 Elements, compounds and mixtures 235


Grouping elements
It is often convenient to group objects Non-metals
that have features in common. Only 22 of the elements are non-
Shops provide a good example of metals. At room temperature, 11of
this. In a department store, the them are gases, 10 are solid and
goods are grouped so that you know 1 is liquid. The solid non-metals
where to buy them. You go to the have most of the following features

clothing section for a new pair of in common:

jeans, to the jewellerysection for a They cannot be polished to give
new watch and to the food section a shine like metals; they are
for a packet of potato chips. usually dull or glassy.
Scientists also organise objects They are brittle, which means
into groups. Biologists organise they shatter when they are hit.
living things into groups. Animals They cannot be bent into shape.
Common examples of non-metals
They are usually poor conductors are sulfur, carbon and oxygen.
with backbones are divided
of electricity and heat.
into mammals, birds, reptiles,
They usually melt at
amphibians and fish. Geologists
lowtemperatures. elements that have features of
organise rocks into groups.
both metals and non-metals are
The elements that make up all Metalloids called metalloids. There are eight
substances can also be organised Some of the elements in the non-
into groups. metalloids altogether: boron,
metal group look like metals. silicon, arsenic, germanium,
One example is silicon. While antimony, polonium, astatine
Metals and it can be polished like a metal, andtellurium.
non-metals silicon is a poor conductor of
heat and electricity, and cannot
Scientists have divided the elements be bent or made into wire. Those Metalloids are important
into two main groups: the metals materials often used in electronic
and the non-metals. components of computer circuits.

The metals have several features
in common:
They are solid at room
temperature, except for mercury,
which is a liquid.
They can be polished to produce
a high shine or lustre.
They are good conductors of
electricity and heat.
They can all be beaten or bent
into a variety of shapes. We say
they are malleable.
They can be made into a wire.
We say they are ductile.
They usually melt at high
temperatures. Mercury,
whichmelts at 40C, is

236 Science Quest 8


Looking for similarities 8

AIM To describe the characteristics of a variety

of elements

Shiny or Does it Does it conduct

Element dull? bend? electricity?



Connect your element sample into this circuit.

Power supply


5 Element to
be tested

7 Contacts
(alligator clips)



sheet 7.2 Metals and non-metals

7 Elements, compounds and mixtures 237


Patterns, order
Chemical name tags

As more and more elements were being Because some elements had things in common,
discovered, the early scientists began to find scientists decided to organise them into groups. It took
that some of them had things in common. a long time and a lot of experimenting to work out the
groups. A Russian scientist called Dmitri Mendeleev
finally worked out a system for grouping the elements.
Alkali Alkaline His system is called the periodic table and a modern
metals earth metals version is used by scientists today.

Group 1 Group 2
3 4 1 2 Atomic number
Lithium Beryllium Hydrogen Helium Name
Period 2 Li Be H He
Period 1 Symbol
6.94 9.02 1.008 4.003 Relative atomic mass
11 12
Sodium Magnesium Transition metals
Period 3 Na Mg Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 Group 9 Group 10
22.99 24.31
19 20 21 22 23 24 25 26 27 28
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel
Period 4 K Ca Sc Ti V Cr Mn Fe Co Ni
39.10 40.08 44.96 47.87 50.94 52.00 54.94 55.85 58.93 58.69
37 38 39 40 41 42 43 44 45 46
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium
Period 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd
85.47 87.62 88.91 91.22 92.91 95.96 98.91 101.1 102.91 106.4
55 56 5771 72 73 74 75 76 77 78
Caesium Barium Lanthanides Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum
Period 6 Cs Ba Hf Ta W Re Os Ir Pt
132.9 137.3 178.5 180.9 183.8 186.2 190.2 192.22 195.1

87 88 89103 104 105 106 107 108 109 110

Period 7 Francium Radium Actinides Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium
Fr Ra Rf Db Sg Bh Hs Mt Ds

57 58 59 60 61 62 63 64
The periodic table. Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium
Elements 192 all occur La Ce Pr Nd Pm Sm Eu Gd
naturally. Those from 138.91 140.122 140.91 144.24 (145) 150.4 151.96 157.25
element 93 onwards
have been made in Actinides
laboratories and are all 96
89 90 91 92 93 94 95
radioactive. Those from Curium
Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium
element 112 onwards are Cm
Ac Th Pa U Np Pu Am
not shown in this table. (243) (247)
(227) 232.04 231.04 238.03 237.05 (244)

238 Science Quest 8

Looking for similarities
A vertical column on the periodic table is called a
group. Elements in the same group on the periodic REMEMBER
table always have some features in common. 1
Sometimes these common features are easy to
observe, but some of the similarities are not so
obvious. For example, neon and argon are gases that 2
do not change when mixed with other elements
except under extreme circumstances. They are said
to be inert. These two gases are found in the last 3
group of the periodic table along with three other

inert gases. Thegroupcontaining the inert gases is

called the noblegas group.

The group number corresponds

to the number of electrons in the
outershell. Halogens Noble gases
The period number refers to the
number of the outermost shell Group 13 Group 14 Group 15 Group 16 Group 17 Group 18
containing electrons.
er 5 6 7 8 9 10
New radioactive elements are still Boron Carbon Nitrogen Oxygen Fluorine Neon
being produced the most recent B C N O F Ne
one at the time of publication was 10.81 12.01 14.01 16.00 19.00 20.18
ic mass
element 118.
13 14 15 16 17 18
Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Group 9 Group 10 Group 11 Group 12 Al Si P S Cl Ar
26.98 28.09 30.97 32.06 35.45 39.95
27 28 29 30 31 32 33 34 35 36
Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Co Ni Cu Zn Ga Ge As Se Br Kr
58.93 58.69 63.55 65.38 69.72 72.63 74.92 78.96 79.90 83.80
45 46 47 48 49 50 51 52 53 54
Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Rh Pd Ag Cd In Sn Sb Te I Xe
102.91 106.4 107.9 112.4 114.8 118.7 121.8 127.8 126.9 131.3
77 78 79 80 81 82 83 84 85 86
Iridium Platinum Gold Mercury Thallium Lead Bismuth Polonium Astatine Radon
Ir Pt Au Hg Tl Pb Bi Po At Rn
192.22 195.1 197.0 200.6 204.4 207.2 209.0 (209) (210) (222)

109 110 111 112 Metals Non-metals

Meitnerium Darmstadtium Roentgenium Copernicium
Mt Ds Rg Cn

63 64 65 66 67 68 69 70 71
Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium
Eu Gd Tb Dy Ho Er Tm Yb Lu
151.96 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97

95 96 97 98 99 100 101 102 103

Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium
Am Cm Bk Cf Es Fm Md No Lr
(243) (247) (247) (251) (254) (257) (258) (255) (256)

7 Elements, compounds and mixtures 239


Making molecules
The naturally occurring elements are the building blocks compoundcarbon dioxide, one carbon and two
of everything in our world. The atoms of various elements oxygen atoms are joined in every molecule. Atoms
can be joined in a wide variety of ways to produce can join to form small or large molecules of many
many compounds. Elements and compounds can be different shapes.
combined in many ways to make countless mixtures. Some compounds are not made up of molecules.
Atoms can join, or bond, in many different ways. Instead the atoms bond by lining up one after the

Insome substances, atoms are joined in groups other. Sodium bonds to chlorine, which bonds to
called molecules. For example, in oxygen gas, sodium and so on. Common table salt is an example
oxygen atoms are joined in groups of two. In the of a substance that is bonded in this way.


Mix n match
AIM To model the molecules of a variety of compounds

A green diamond represents an

atom of oxygen. Together, two
diamonds represent a molecule
of oxygen.

1.5 cm

2 cm
2 cm

2 cm


Cut these 2 cm 2 cm
shapes from 1
coloured paper.

2 cm 2


240 Science Quest 8

(b) plastic glass, polystyrene foam for packaging and
cups, note money, cases for electronic appliances such
as computers and televisions, clothing, glues, shopping
bags, sports equipment and even tea bags!



Models representing the molecules of
the compounds (a)carbon dioxide, (b) (c)
water and (c) methane. The black balls
represent carbon; the red, oxygen; and
the white, hydrogen.


Compounds of today
and tomorrow
Polymer is the name given to a compound made
of molecules that are long chains of atoms. Most
polymers are made up of chains containing carbon
atoms. Plastics are synthetic polymers, while cotton
and rubber are examples of natural polymers.
Although scientists first developed polymers in
laboratories in the 1800s, it was not until after World
War II that most modern polymers were invented.
Modern polymers are used in food wrapping, paint,


sheet The periodic table
7.4 
atomic structure

Compound Formula Number of elements Names of elements

Copper sulfate CuSO4 3 Copper, sulfur, oxygen
Zinc sulfide ZnS
Ammonia NH3
Sulfuric acid H2SO4
Hydrochloric acid HCl
Table salt NaCl

7 Elements, compounds and mixtures 241


Carbon: Its everywhere

Thats carbon? dioxide and water to make sugar. Sugar is a compound
made up of carbon, hydrogen and oxygen atoms. Plants
Carbon is a most amazing element. It is found naturally use the sugar to make other substances and for energy
in three different forms. One form is diamond, another to grow. Animals eat plants or plant-eating animals. The
is graphite (the lead in lead pencils), and the third is carbon atoms then become part of the animals bodies.
called amorphous carbon (coal, charcoal and soot). Carbon atoms in the bodies of living things return to the
Diamond is the hardest substance known and is used

air in several ways: respiration, decomposition and burning.

to make drill tips and cutting tools. The three forms are Respiration is a process that occurs in the cells of
different from each other because the carbon atoms are every living thing, from a microscopic water plant
joined in different ways. to a humpback whale. Respiration releases energy
Carbon is found combined with other elements in a and produces carbon dioxide. The carbon dioxide
huge range of compounds. No other element forms as released by the cells in your body is taken by your
many different types of compounds as carbon. Carbon blood to your lungs. The carbon dioxide that you
is found in everything from the skin of an elephant to breathe out contains carbon atoms that were once
paint on the walls! part of your body.
Decomposition is what happens when plant or
The chemistry of life animal material breaks down, such as in a compost
All living things are made up of compounds including heap or after something is buried. Microscopic
proteins, fats and carbohydrates. The main element in living creatures called decomposers absorb some
these compounds is carbon. Carbon is not found only of the substances in the dead material and release
in living things, but also in the air in carbon dioxide and carbon dioxide to the air by respiration.
under the sea in limestone. The carbon atoms in carbon When substances containing carbon are burned,
dioxide were once carbon atoms in living things. The carbon dioxide is released. Coal, natural gas and oil
carbon atoms in living things will eventually become are all fuels formed from living things, and contain
carbon atoms in the air or carbon atoms in limestone carbon atoms. Fuels are combustible; that is, they
under the sea. The illustration below shows how nature are easily ignited. When these fuels are burned in
constantly recycles carbon atoms. homes, cars, factories and power stations, carbon
Plants take in carbon dioxide through their leaves and, dioxide is released into the air. Bushfires also release
in a process known as photosynthesis, use the carbon carbon dioxide back to the air.

Plants absorb
some oxygen.
Plants absorb
Both plants CO2 during
and animals the day.
release CO2. Plants release
oxygen during Fossil fuels
the day. release CO2
when burned.

Animals absorb Petroleum Oil

carbon when
they eat plants.
The flow of carbon atoms
through the environment
Gas Coal

242 Science Quest 8


Looking for carbon

AIM To test for the presence of carbon in a range




Substance Observations Is carbon present?

Cotton wool


Material content (%) (MJ)
Wood 11 17.9
Brown coal 73 29.5
2 Black coal 80 35.9
Natural graphite 90 39



8 State

Solid Liquid Gas

7 Elements, compounds and mixtures

ELEMENTS AND ATOMS recognise that the properties of compounds are different
from the elements that make them up
describe some common chemical elements
use the formulas of simple compounds to identify the
recall the chemical symbols of some common elements
elements that make them up
identify some of the dangers associated with some
chemical elements model the arrangement of atoms in the molecules of
some compounds
model the structure of the atom and describe the
characteristics of the three main particles identify and describe some common compounds and
recall that each chemical element is identified with their uses
auniqueatomic number, which is equal to the number
ofprotons in its nucleus SCIENCE AS A HUMAN ENDEAVOUR
distinguish between metals, non-metals and metalloids
describe how the understanding of the particles that make
identify similar properties of groups of elements in the up all matter has changed over time

periodic table
explain how the ideas about elements and the atom
havechanged over time
COMPOUNDS AND MIXTURES describe the contributions of some of the scientists
distinguish between elements, compounds and mixtures whohave added to our knowledge of the atom and
recall that the atoms in compounds are bonded very the elements
tightly together recognise the impact of new scientific discoveries and
recall that elements can be separated from compounds technology on our understanding of the atom, elements
onlythrough a chemical reaction and compounds

Answers for this chapter can be Interactivities
found online in your eBookPLUS. Its elementary!
revelation game
Online section In this revelation game,
you must identify common
This section of the chapter can be found online in
elements from their
symbols to reveal the full
7.8 Thinking tools: Affinity diagrams and periodic table. You must
cluster maps answer quickly to complete
the game in time.
Individual pathways Searchlight ID: int-0229
Activity 7.1 Activity 7.2 Activity 7.3 Making molecules
Investigating Analysing Investigating In this interactivity, you
substances substances substances further will use carbon, chlorine,
doc-6069 doc-6070 doc-6071 hydrogen, nitrogen and
oxygen atoms to create
the correct models of
FOCUS activity a series of chemical
Access more details about focus activities for formulae. Instant feedback
this chapter in your eBookPLUS.
is provided.
Searchlight ID: int-0228
Add Lavoisier and
hydrogen watch a video
from The story of science FPO
about the discovery of
the elements.
Searchlight ID:

244 Science Quest 8

LOOKING BACK Link to assessON for questions to
test your readiness FOR learning, your
1 About 2500 years ago, Democritus suggested what all progress AS you learn and your levels OF
substances were made up of. achievement.
(a) In what way was Democritus idea about substances
the same as the model that scientists currently use to
describe substances? 10 Complete the following table to summarise what you know
(b) Suggest why most thinkers of the time disagreed with about metals and non-metals.
2 Copy and complete the following table, which describes the Metals Non-metals
structure of atoms.
Conduct electricity well
Size and Conduct heat well
Part of weight Electric
atom Location (relative) charge Surface features

Large Positive State at room temperature

Neutron Malleable

Outside the nucleus Ductile

3 If a neutral atom has 12 protons, how many electrons
does it have? 11 Which of the elements iron, lead, hydrogen, oxygen, silicon,
4 What takes up most of the space in an atom? uranium and sodium are:
5 Identify the one feature that every single atom of the (a) metals
element sodium has in common. (b) metalloids
(c) non-metals?
6 What is the atomic number of each of the
following elements? 12 (a)Which element is used inside illuminated signs like the
(a) Hydrogen one below?
(b) Carbon
(c) Uranium
7 How many protons does each of the elements listed in
question 6 have in its nucleus?
8 How many electrons does each of the elements listed in
question 6 have in its nucleus?
9 Make a copy of the diagram of the atom below and label an
electron and the nucleus. Answer the following questions.
(a) How many protons does this atom have?
(b) How many neutrons does this atom have?
(c) How many electrons does this atom have?
(d) What is the atomic number of this atom?
(e) Describe one use of the element that is made up of
these atoms.

+ (b) To which group in the periodic table does this

element belong?
13 What event must take place in order to separate a
compound into separate elements?
14 How are the molecules in polymers different from the
molecules of other compounds?
15 Complete the table on the next page to indicate whether the
substances listed are elements, compounds or mixtures.
Also indicate why you made that decision.

7 Elements, compounds and mixtures 245

18 Each of the diagrams below represents one of the bits that
matter that make up substances.
compound or Why do you
Substance mixture think so? A B
Carbon dioxide C D

Sea water
Pure water

Iron E F
Table salt (NaCl)

16 Which of the bits that matter is represented by each of the G H

cartoons below?



19 Which of the diagrams represents:

(a) an atom of an element
(b) a molecule of an element
17 What do diamonds, the lead in pencils and coal have (c) a molecule of a compound?
in common? 20 Most of the substances around you are compounds
and mixtures.
(a) What differences could be observed between a mixture
of hydrogen and oxygen, and a compound of hydrogen
and oxygen?
(b) Explain the difference between a compound and a
mixture in your own words.
21 Respiration is a chemical reaction in which carbon dioxide
is produced.
(a) Where in your body does respiration take place?
(b) What is released during respiration apart from
carbon dioxide?
(c) Suggest how the carbon atoms in carbon dioxide enter
your body.
22 Why doesnt water appear in the periodic table?

sheet 7.5 Summing up

246 Science Quest 8

ICT Activity
The guidelines for the video submission from the Channel 55
website are as follows:
The video must be between four and five minutes in length.

Science TV The target audience of Science TV is between 8 and

14years old.
SEARCHLIGHT ID: PRO-0090 At least two people must be shown on camera.
The video must be in the form of a chemistry segment that
Scenario explains one of the following:
a. What is the difference between a physical change and
In the media world, programs that combine entertainment
achemical change?
and education are known as edutainment. With the
b. What are elements, compounds and mixtures?
success of edutainment programs such as Mythbusters
c. How would we separate a mixture of iron filings, sand,
(SBS/7Mate), Scope (Network 10) and The ExperiMentals

copper sulfate and chalk dust?

(ABC), it seems that science is attracting a bigger share
At least one experiment must be shown being performed
of the television market than many network executives
in the segment the experiment must be relevant to the
would have expected. Now, your local TV network
segment and safe to perform (i.e. no explosions and no
Channel 55 has decided to jump on the science as
dangerous fumes produced).
edutainment bandwagon and has announced that next
The segment should be engaging and informative. It
year it will develop a program called Science TV. should have an introduction (either a scenario played out
To make Science TV more appealing to a younger or a discussion between the presenters), an experiment to
audience, the developing executives of the program either test or demonstrate an idea, an explanation of the main
want it to be presented by a team of school students, concepts involved and a resolution that ties back into the
who will do all of the introductions, explanations and original scenario or discussion. Remember: the main idea is
experiments for each of the segments. It is important toshow that science is FUN!
that the right team of students is found or the program
will be canned after only a few episodes, so Channel 55 Process
has announced that it is accepting online audition files Open the ProjectsPLUS application for this chapter located
from groups of students who think they have what it in your eBookPLUS. Watch the introductory video lesson
takes to be the Science TV stars. and then click the Start Project button to set up your
project group. Save your settings and the project will be
Your task launched. The rest of the process is outlined online in your
Your group is going to put together a video submission ProjectsPLUSapplication.
that you could send to the Channel 55 developers to
showcase how suitable you would be as the stars of
Science TV.

7 Elements, compounds and mixtures 247