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Elements and Compounds
It follows that
compounds contain twoor more types of atom.
The water molecule contains two
hydrogen atoms bonded to one
oxygen atom, so the formula is H2O.
Elements are materialsmade up of one type of
atom only. Hydrogen molecule contains
two hydrogen atoms bonded
together, so the formula is H2.
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Compounds: Water
Compounds are produced when elements combine. For
example, water is produced in the following reaction.
Word Equation
Hydrogen + Oxygen Water
+ +
Two water molecules react with one oxygen molecule to give water.
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Compoundsnot mixtures
The atoms in compounds are NOT
mixed together. A mixture of hydrogenand oxygen would look like:
They become bondedtogether during a chemical
reaction. Because of this compounds have properties that
are verydifferent to the elements that they are made from.
HYDROGEN
Flammable gas.
OXYGEN
Gas in which many
substances burn.
WATER
Liquid that extinguishes
most fires.
+
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Compoundsnot mixtures
Black solid
used as
barbecue
fuel
Gas in
which
many
substancesburn
Gas used in
fizzy drinks and
fire
extinguishers
carbon + oxygen carbon dioxide
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Naming Simple compounds.
It is easy to name simple compounds of metals and non-metals.
1. Write down the name of the metal2. Write down the name of the non-metal but change
the ending to ide.
oxygencalcium
sulphursilver
brominecopper
Name of compoundElement 2Element 1
copper bromide
silver sulphide
calcium oxide
1) magnesium 2) oxygen =magnesium
oxide
1) sodium 2) chlorine =sodium
chloride
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Name the compound formed from these elements
nitrogenlithium
sulphurzinc
iodinenickel
brominealuminium
oxygentin
chlorinesodium
nitrogenmagnesium
sulphuriron
Name of compoundElement 2Element 1
iron sulphide
magnesium nitride
sodium chloride
tin oxide
aluminium bromide
nickel iodide
zinc sulphide
lithium nitride
Naming Simple compounds.
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Naming more complicated Compounds
Many compounds contain more than twoelements. Naming them can get complicated butfor those containing two elements plusoxygenthe name ending usually changes to ate.
oxygenbrominealuminium
oxygensulphurcopperoxygen
oxygen
oxygen
Element 3
nitrogensodium
magnesium nitratenitrogenmagnesium
nickel sulphatesulphurnickel
Name of compoundElement 2Element 1
sodium nitrate
copper sulphate
aluminium bromate
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The composition of compounds.
Compounds are very different to the elements from
which they are made but there is another way inwhich compounds are different to mixtures.
In a mixture you can add any amount of the
ingredients.
Compounds always contain a definite amount of eachelement. They have a fixed composition.
This is not really surprising as looking at the word
equations you will have seen they always have adefinite number of element atoms joined together.
Na Cl O OC Mg OO
H
H
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The formula of compounds
This means that every compound can have a
formula that tells us how many of each type of atom
are present. We include small slightly dropped
numbers if there are more of one atom than the
other.
Water
One oxygen atom
Two hydrogen atoms
Formula H2O
O
H
H
Carbon dioxide
One carbon
atom
Two oxygen
atoms
FormulaCO2
O OC
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What is the formulae
of each of thecompounds shown?
(As with names, put
the metal first.)
2. Lithium Oxide
LiO
Li
? oxygen atom
? lithium atoms
Formula
?
3. Aluminium chloride
? aluminium atom
? chlorine atomsFormula
Al ClCl
Cl
1. Titanium oxide
? titanium atom
? oxygen atomsFormula
Ti OO
1 titanium atom
2 oxygen atoms
Formula
TiO2
1 oxygen atom
2 lithium atoms
Formula
Li2O
1 aluminium atom
3 chlorine atomsFormula
AlCl3
Activity
The formula of compounds
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What is the formulaeof each of the compounds
shown?
Silicon chloride
? silicon atom
? chlorine atomsFormula
Si ClCl
Cl
Manganese oxide
? manganese atom
? oxygen atomsFormula
Mn OO
1 manganese atom
2 oxygen atoms
Formula
MnO2
1 silicon atom
4 chlorine atoms
Formula
SiCl4
Cl
Aluminium oxide
? aluminium atom
? oxygen atoms
Formula
Al
OO O
2 aluminium atom
3 oxygen atoms
Formula
Al2O3
Al
Activity
The formula of compounds
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Word equations can be used to describe anychemical change. (i.e. any process where the atoms
become joined (bonded) in different ways).
The steps are:
1. Write down the name of the reactant(s) linking
them with a +sign if there is more than one.
2. Write down an arrow
3. Write down the names of the products linkingthem with a +sign if there is more than one
Word Equations
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It hasnt just mixed.
It has reacted and atoms are joined differently.
Write out word equations for this reaction
Lead reacts with oxygen to form lead oxide
Lead + oxygen lead oxide
Lead Lead oxide
Why is lead oxide so different to both lead and oxygen?
Activity
Word Equations
A ti it
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Write out word equations for the following
reactions.1. Limestone (calcium carbonate) is heated to make
calcium oxide and carbon dioxide.
2. Magnesium reacts with hydrochloric acid to makemagnesium chloride and hydrogen.
3. Methane is burnt to make carbon dioxide andwater.
calcium carbonatecalcium oxide +carbon dioxide
magnesium + hydrochloric acid magnesium chloride + hydrogen
methane + oxygencarbon dioxide + water
Activity
Word Equations
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Mixtures
Mixtures are, as the name indicates, mixedrather thanreacted together.
This means that, unlike compounds:1 They do not have to have any particularproportions of the various ingredients.
2 Their properties are often an average of theproperties of their ingredients. (eg. a mixture of ablack and white powder is grey!)
sea water: a mixture
of salts and water
3 They are mixed, not bonded, and
so are usually not too hard toseparate back into their ingredients.
(For example, it is easy to get salt
from sea water.)
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S i Mi
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Immiscible liquids
Immiscible means doesnt mix and so we are talkingabout mixtures like water with cooking oil or water with
petrol.
On a small scale you can simply remove the top layer
using a pipette.
oil
water
water oil
Separating Mixtures
S ti Mi t
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Miscible liquidsMiscible means does mix and so we are talking about
mixtures like water and alcohol or petrol with kerosine.
These are separated by boiling them as it is unlikely that
they will boil at exactly the same temperature.
In order to get back the liquids we use a condenser. This
is a tube that has cold water circulating through the
outside. It cools down vapours and condenses them back
to a liquid. Substances with low boiling points collect first,
while those with higher boiling points collect later.
Separating Mixtures
Mi ibl li id
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condenser
electric
heatercollection
beaker
water in
water out
thermometer
Distillation Equipment
Miscible liquids
S ti
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Separations
How would you get this?
Mixture Wanted Method
Glass and water glass
Sea water saltSea water water
Cooking oil & water cooking oil
Alcohol and water alcohol
filter
evaporate
distil
pipette
distil
S ti E i t
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John has been given a mixture of salt, sand and water.He needs to separate them but cannot remember how.
Can you help him?
Write an experimental plan for John to follow so that hecan have the sand, salt and water in separate
containers.
Make sure you start off by telling him what equipmenthe will need.
Then he will need a step by step plan that is easy to
follow.
Separation Experiment
S ti iti
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Summary activities
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1. Which of these is a compound?
A. bromine
B. copperC. carbon dioxide
D. uranium
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2. Which of these best describes a
compound?
A. Two or more atoms bonded together.
B. Two or more elements mixed together.C. Two or elements bonded together.
D. Two or more types of molecule mixed
together.
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3. Which of these could best describe compounds?
Substances that:
A. are similar to the elements that they are made
from.
B. can be formed when elements react together.
C. can be formed when elements decompose into
two or more new substances.
D. substances with symbols in the Periodic Table.
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4. What would be the name of acompound formed from sulphur, oxygenand zinc?
A. sulphur zincideB. sulphur zincate
C. zinc sulphide
D. zinc sulphate
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5. What would be the formula of acompound containing two aluminium
atoms for every three sulphur atoms?
A. Al2S3 B. Al3S2
C.Al2S3 D.Al3S2
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6. How would you separate a mixture ofwater and alcohol. (Two miscible liquids)
A. filteringB. chromatography
C. evaporation
D. distillation
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7. What is the main technique you woulduse when separating a mixture of saltand sand?
A. filtering
B. chromatography
C. evaporation
D. distillation
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8. Use the chromatogram to decide
which dyes are in the ink.
A B C D Ink