© Boardworks Ltd 2003 Elements and Compounds two or more types of atom. It follows that compounds contain two or more types of atom. The water molecule.

© Boardworks Ltd 2003

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.


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.


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.

+


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


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


Name the compound formed from these elements

nitrogenlithium

sulfurzinc

iodinenickel

brominealuminium

oxygentin

chlorinesodium

nitrogenmagnesium

sulfuriron


iron sulfide

magnesium nitride

sodium chloride

tin oxide

aluminium bromide

nickel iodide

zinc sulfide

lithium nitride

Naming Simple compounds.


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


sodium nitrate

copper sulfate

aluminium bromate


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


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


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



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



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


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


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


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.)




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


condenser

electricheater

collectionbeaker

water in

water out

thermometer

Distillation Equipment

Miscible liquids


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


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


Summary activities


1. Which of these is a compound?

A. bromine

B. copper

C. carbon dioxide

D. uranium


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.


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.


4. What would be the name of a compound formed from sulphur, oxygen and zinc?

A. sulfur zincideB. sulfur zincateC. zinc sulfideD. zinc sulfate


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


6. How would you separate a mixture of water and alcohol. (Two miscible liquids)

A. filtering

B. chromatography

C. evaporation

D. distillation


7. What is the main technique you would use when separating a mixture of salt and sand?

A. filteringB. chromatographyC. evaporationD. distillation


8. Use the chromatogram to decide which dyes are in the ink.

A B C D Ink

© Boardworks Ltd 2003 Elements and Compounds two or more types of atom. It follows that compounds contain two or more types of atom. The water molecule.

Documents

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formula of compounds

composition of compounds

complicated compounds

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