COMPOUNDS
Why are there so many compounds?
How can we show the contents of a compound?
Name
Class
Date
Teacher
____________________________
__________
__________
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CORE BOOKLET 3
1
COMPOUNDS
At the end of this topic I should:
Tick
know that new substances called compounds are formed when
two or more different elements combine together and that each
compound has its own chemical formula
be able to name the elements present, and the number of atoms
present in a given chemical formula
be able to write chemical formulae for compounds formed
between group I or II elements and elements of group VI or
VII, using the formulae of ions that they contain.
be able to write formulae for ionic compounds containing
hydroxide, nitrate, sulphate or carbonate ions using the
formulae of the ions they contain
Be able to draw and interpret space filler type diagrams for
simple molecules such as for methane
Summary of content
This is a short booklet about compounds. Compounds are
formed when two or more elements react together.
The reason that elements react is to get full outer shells of
electrons.
When elements have full outer shells of electrons they are
more stable.
The number of electrons that an element needs to gain or lose
to achieve full outer shells has an impact on the proportions
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that react together. The proportions of elements that react
together to form a compound are represented by chemical
formulae.
Take for example the compound magnesium chloride.
Magnesium has an electron arrangement of 2:8:2, chlorine has
an arrangement of 2:8:7. Magnesium will donate its two outer
electrons to two chlorines. That way, both magnesium and the
two chlorine atoms can become stable as they now have full
outer shells. The chemical formula for magnesium chloride is
MgCl2. As part of this booklet you will be taught an easy way
of writing your own chemical formulae.
Naming compounds
Naming compounds is relatively simple. If they contain two
elements, the first will keep its name, the second will end in
ide. If your compound contains two elements plus oxygen the
first will keep its name, the second will end in ate. Some
compounds such as water have common names such as water.
Technically water should be called hydrogen oxide, you’d have
a few funny looks if you went into a shop to ask for a bottle of
hydrogen oxide.
Space filler diagrams
Finally, as part of this topic you’re expected to be able to draw
and interpret space filler type diagrams for simple molecules
such as for methane
. This means that you
should be able to look at this diagram and be able to work out
that the chemical formula is CH4.
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Why are there so many compounds?
Every new compound is an entirely new substance. In most
cases a compound will be completely different to the elements
that make it up. If you think of how many words you can make
by combining 26 letters of the alphabet, think how many
combinations you can make from 100 elements!
Revision
In the previous booklets you have been given chemical formulae
for compounds and have used them to write equations. In this
booklet you will find out how to work out some chemical
formulae for yourselves. Let’s go back to basics….
Naming simple compounds
Compounds containing two compounds have two names. The
second name ends in –ide. If you see ide then you know that
you are looking at a compound. The first name will be the name
of the first element.
E.g a compound contains sodium and oxygen, it will be called
sodium oxide. We could write this as what is known as a word
equation;
Sodium
+
oxygen
sodium oxide
 The left hand side tells us what we’ve started with (the
reactants).
 The right hand side tells us what has been made (the
product)
 The arrow tells us that a chemical reaction has taken
place.
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Name the following compounds!
1. Sodium
+
chlorine
2. Magnesium
+
oxygen
3. Potassium
+
nitrogen
4. Lithium
+
sulphur
5. aluminium
+
iodine
Write down the names of the elements present in the following
compounds;
1. Calcium fluoride
=
7. lithium iodide
=
8. sodium nitride
=
9. aluminium phosphide =
10. potassium chloride =
Compounds containing two elements plus oxygen
Compounds containing two elements plus oxygen end in –ate.
For example compound 1 (above) would be called sodium
chlorate if it contained sodium, chlorine and oxygen.
5
Name compounds 3, 4 and 5 (above) assuming they contained
oxygen as well as the two elements mentioned:3.
4.
5.
Write down the names of the elements present in the following
compounds;
6. Calcium fluorate
=
7. Lithium iodate
=
8. Sodium nitrate
=
9. Aluminium phosphate =
10. Potassium chlorate =
Compounds with common names
Chemistry is a very old subject which used to be known as
ALCHEMY. Alchemy began as age old scientists tried to
turn lead into gold.
Alchemists never did turn lead into gold but as they
experimented they discovered many other substances which
they gave common names to rather than naming them
properly as you’ve done above. Many of these common names
are still used today. See if you can match up the proper
names with their common names on the following page, the
clues are in the pictures:
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Hydrogen oxide
carbon dioxide
Nitrogen hydride
sulphuric acid
Carbon oxide
water
Carbon oxide
methane
Hydrogen sulphate
ammonia
Hydrogen chloride
hydrochloric acid
Carbon hydride
carbon monoxide
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Chemical formulae for compounds
When elements combine to form compounds they do so in
specific proportions.
What do I mean by proportion?
On a human the proportion of noses to legs is1:2. This is
because for every 1 nose there will be 2 legs.
What is the proportion of hydrogen to oxygen atoms in a
water particle?
The ratio or proportion of hydrogen to oxygen is 2:1. We
therefore write that the chemical formula for water is H2O.
Writing chemical formulae
Can you figure out the chemical formulae for the following:
1.
this is ammonia where large circle represents the nitrogen, the small
circles the hydrogen,
Formula for ammonia =
8
2.
Formula for methane =
3.
Formula for carbon dioxide =
4.
Formula for carbon monoxide =
5.
Formula for hydrochloric acid =
6.
Formula for magnesium chloride =
7.
Formula for sodium chloride =
9
8.
Formula for copper carbonate =
9.
Formula for sulphuric acid =
Complete the poem using your formula;
Johny was a chemist
but Johny is no more
for what he thought was H20
was _______________
10.
Formula for copper sulphate =
10
Using ions to work out your own chemical formulae
At the back of your G.C.S.E exam paper you will be given the following list
of ions. At this stage it’s not really necessary to be told what an ion is.
I’ll simply say that they are formed because atoms lose or gain electrons
to form full outer shells making themselves more stable. As they do this
the protons and electrons no longer cancel each other out and the atom
becomes charged. A charged atom is called an ion. The whole process is a
little like what happens during static electricity.
Positive ions
Name
Aluminium
Ammonium
Barium
Calcium
Copper (II)
Hydrogen
Iron (II)
Iron (III)
Lithium
Magnesium
Nickel
Potassium
Silver
Sodium
Negative ions
Formula
Al
NH4+
Ba2+
Ca2+
Cu2+
H+
Fe2+
Fe3+
Li+
Mg2+
Ni2+
K+
Ag+
Na+
3+
Name
Bromide
Carbonate
Chloride
Fluoride
Hydroxide
Iodide
Nitrate
Oxide
Sulphate
Formula
BrCO32ClFOHINO3O2SO42-
As you can see from the table there are also collections of atoms that
can have an overall charge such as ammonium, sulphate, carbonate. These
collections are called compound ions. If there is more than one compound
ion in a chemical formula it is put into brackets e.g aluminium sulphate is
Al2(SO4)3 as there are two aluminiums and 3 sulphates.
If you wanted to work out the chemical formula for a compound simply
swap down the superscript number in front of the charge to make it
subscript after the symbol.
E.g
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Magnesium chloride would be
Mg2+
Cl -
MgCl2


No number in front of the charge for chlorine means 1
You never write the positive/negative charges in the final chemical
formula because the formula will always be such that charges are
cancelled out.
E.g. 2
Aluminium sulphate would be
Al3
+
SO4
2-
Al2(SO4)3
Task
Work out the chemical formulae for the following, show your working out
to the right of the example.
1.Aluminium Chloride
2. Copper oxide -
Remember a chemical formula is a ratio so if the two numbers being swapped down
are the same they will cancel one another out.
3.Lithium oxide
4.Silver chloride
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5.Iron (II) chloride
6.Iron (III) chloride
7.Calcium fluoride
8.Barium oxide
9.Lithium sulphate
10.Aluminium sulphate
11.Copper(II) hydroxide
12.Calcium carbonate
13.Ammonium oxide
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14.Ammonium hudroxide
15.Potassium oxide
16.Potassium iodide
17.Nickel chloride
18.Silver sulphate
19.Sodium sulphate
20.Iron (III) carbonate
CONGRATULATIONS!
YOU CAN NOW WRITE YOUR OWN
CHEMICAL FORMULAE. IT’S ALSO USEFUL TO LEARN A FEW
COMMON ONES SO THAT YOU’LL ALWAYS HAVE THEM AT YOUR
FINGER TIPS.
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Key words
Superscript
Subscript
Element
Protons
Compound
Chemical formula
superscript is a number, figure, or symbol that
appears above the normal line of type.
subscript is a number, figure, or symbol that
appears below the normal line of type.
an element is a substance containing atoms that
are all identical. The reason that the atoms are
identical is that they all contain the same
number of protons.
positive particles contained in the central
nucleus of an atom.
two or more elements chemically bonded
together in fixed proportions represented by a
chemical formula.
A chemical formula shows the ratio of atoms in
an element or compound.
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