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Elements and Compounds
It follows that compounds contain two two or more types of atom.or more types of atom.
The water molecule contains two hydrogen atoms bonded to one
oxygen atom, so the formula is H2O.
Elements are materials made up of one type of one type of atom only.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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Compounds – not mixtures
The atoms in compounds are NOT mixed together. A mixture of hydrogen and oxygen would look like:
They become bondedbonded together during a chemical chemical reaction. reaction. Because of this compounds have properties that are veryvery different 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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Compounds – not mixtures
Black solid used as
barbecue fuel
Gas in which many substances
burn
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
sulfursilver
brominecopper
Name of compoundElement 2Element 1
copper bromide
silver sulfide
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
sulfurzinc
iodinenickel
brominealuminium
oxygentin
chlorinesodium
nitrogenmagnesium
sulfuriron
Name of compoundElement 2Element 1
iron sulfide
magnesium nitride
sodium chloride
tin oxide
aluminium bromide
nickel iodide
zinc sulfide
lithium nitride
Naming Simple compounds.
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Naming more complicated Compounds
Many compounds contain more than two elements. Naming them can get complicated but for those containing two elements plusplus oxygen the name ending usually changes to –ate.–ate.
oxygenbrominealuminium
oxygensulfurcopper
oxygen
oxygen
oxygen
Element 3
nitrogensodium
magnesium nitratenitrogenmagnesium
nickel sulfatesulfurnickel
Name of compoundElement 2Element 1
sodium nitrate
copper sulfate
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 in which compounds are different to mixtures.
• In a mixture you can add any amount of the ingredients.
• Compounds always contain a definite amount of each element. They have a fixed composition.
• This is not really surprising as looking at the word equations you will have seen they always have a definite 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.
WaterWater
One oxygen atom
Two hydrogen atoms
Formula HH22OO
O
H
H
Carbon dioxideCarbon dioxide
One carbon atom
Two oxygen atoms
Formula COCO22
O OC
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What is the formulae of each of the compounds shown?(As with names, put the metal first.)
2. Lithium Oxide2. Lithium Oxide
LiO
Li
? oxygen atom
? lithium atoms
Formula
??
3. Aluminium chloride3. Aluminium chloride
? aluminium atom
? chlorine atomsFormula
Al ClCl
Cl
1. Titanium oxide1. Titanium oxide
? titanium atom
? oxygen atomsFormula
Ti OO1 titanium atom
2 oxygen atomsFormula
TiOTiO22
1 oxygen atom
2 lithium atoms
Formula
LiLi22OO
1 aluminium atom
3 chlorine atomsFormula
AlClAlCl33
Activity
The formula of compounds
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What is the formulaeof each of the compoundsshown?
Silicon chlorideSilicon chloride
? silicon atom
? chlorine atomsFormula
Si ClCl
Cl
Manganese oxideManganese oxide
? manganese atom
? oxygen atomsFormula
Mn OO1 manganese atom
2 oxygen atomsFormula
MnOMnO22
1 silicon atom
4 chlorine atomsFormula
SiClSiCl44
Cl
Aluminium oxideAluminium oxide
? aluminium atom
? oxygen atoms
Formula
AlOO O
2 aluminium atom
3 oxygen atoms
Formula
AlAl22OO33
Al
Activity
The formula of compounds
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Word equations can be used to describe any chemical 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 arrow3. Write down the names of the products linking
them with a ++ sign if there is more than one
Word Equations
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It hasn’t 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
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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 make magnesium chloride and hydrogen.
3. Methane is burnt to make carbon dioxide and water.
calcium carbonate calcium oxide +carbon dioxide
magnesium + hydrochloric acid magnesium chloride + hydrogen
methane + oxygen carbon dioxide + water
Activity
Word Equations
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Mixtures
Mixtures are, as the name indicates, mixedmixed rather than reacted together.
This means that, unlike compounds: 1 They do not have to have any particular proportions of the various ingredients.
2 Their properties are often “an average” of the properties of their ingredients. (eg. a mixture of a black 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 to separate back into their ingredients. (For example, it is easy to get salt from sea water.)
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Miscible liquids
Miscible 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
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condenser
electricheater
collectionbeaker
water in
water out
thermometer
Distillation Equipment
Miscible liquids
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Separations
How would you get this?
Mixture Wanted Method
Glass and water glass
Sea water salt
Sea water water
Cooking oil & water cooking oil
Alcohol and water alcohol
filter
evaporate
distil
pipette
distil
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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?
Separation Experiment
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Summary activities
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1. Which of these is a compound?
A. bromine
B. copper
C. carbon dioxide
D. uranium
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2. Which of these best 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 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 a compound formed from sulphur, oxygen and zinc?
A. sulfur zincideB. sulfur zincateC. zinc sulfideD. zinc sulfate
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5. What would be the formula of a compound containing two aluminium atoms for every three sulfur atoms?
A. Al2S3 B. Al3S2
C. Al2S3 D. Al3S2
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6. How would you separate a mixture of water and alcohol. (Two miscible liquids)
A. filtering
B. chromatography
C. evaporation
D. distillation
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7. What is the main technique you would use when separating a mixture of salt and sand?
A. filteringB. chromatographyC. evaporationD. distillation
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8. Use the chromatogram to decide which dyes are in the ink.
A B C D Ink