Ch06 elements, compounds & mixtures

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Chapter 6: Elements, Compounds and Mixtures

Transcript of Ch06 elements, compounds & mixtures

Page 1: Ch06 elements, compounds & mixtures

Chapter 6:

Elements, Compounds and Mixtures

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Before we move on,

We have…

Representing the video clip available

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Lesson Outline• recognise that substances can be classified as

elements, compounds and mixtures

• distinguish among elements, compounds and mixtures

• identify an element as the basic building block of matter

• recognise that elements are classified according to their properties

• describe compounds as substances consisting of two or more chemically combined elements

• describe mixtures as two or more elements and/or compounds that are not chemically combined

• classify elements as metals and non-metals based on their characteristic properties

• show an appreciation of the systematic investigation involved in the study of substance

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6.1 Elements

Elements are the simplest kind of matterIt cannot be broken down into simpler substances by chemical reactionsE.g. When you heat oxygen, expose it to light or pass electricity through it, it does not break down and remains as oxygen.

Oxygen

+

= Oxygen

o2

o2

lead

There are more than 110 elements.

Every element is given a name and a chemical symbol.

E.g. Helium = He Chemical symbol takes one or two letters from the name of the element

First letter is always capitalised and the letter that follows is in lower case

For two-letter symbols, they may not always be the first two letters of the name of the element

Oxygen

o2

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There are some cases where chemical symbols take letters from the name of the element in other languages such as Latin, Greek and Arabic.

Name of element

Chemical symbol

Name of element (Language)

Potassium K Kalium (Latin)

Iron Fe Ferrum (Latin)

Copper Cu Cuprum (Latin)

Silver Ag Argentum (Latin)

Tin Sn Stannum (Latin)

Gold Au Aurum (Latin)

Mercury Hg Hydrargyrum (Latinized Greek)

Lead Pb Plumbum (Latin)

Did You Know???

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6.2 Classification of Elements

To make the study of matter easier, scientists have classified the elements.

Classifying elements according to similar chemical properties arranged systematically in a table is called the Periodic Table.

Go to Video 6.1

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Classifying Elements by

StateA simple way to classify elements is to observe their physical states at room temperature.

Lead (solid)

Mercury (liquid)

Chlorine (gas)

Classifying Elements as Metals and Non-MetalsHere are the characteristic properties that are used to classify elements into metals and non-metals:

Metal Non-Metal• shiny appearance• high density• high melting point• good electrical and heat conductor • ductile• malleable• sonorous

• dull appearance• low density• low melting point• poor electrical and heat conductor • non-ductile• brittle• non-sonorous

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Uses of Metals

• Aluminium is used to make aircraft bodies, packaging and cooking utensils because it is light and resists corrosion

• Copper does not react to water and is cheap thus it is used to make water pipes to prevent corrosion. It is also used to make wires as it is a good conductor of electricity.•Silver reflects light so well that it is used to coat glass to make mirrors. Some other uses include jewellery, coins and electrical contacts.

Can you think of more uses of metals?

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Uses of Non-metals

Hydrogen is used

• as rocket fuel• for making margarine• for filling weather balloons

Oxygen is used

• for respiration• for combustion• in oxy-acetylene flames for welding

Carbon is used

• in the formation of living tissues• as a fuel• in pencil leads

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Sodium chloride (salt)

6.3 Compounds

A compound is a substance consisting of two or more different chemically combined elements

Compounds are formed during chemical reactions, where heat and sometimes

light energy is given out or taken in

E.g. H2O (chemical formula of water)

Type of element: Hydrogen

Number of element: 2

Type of element: Oxygen

Number of element: 1

A chemical formula is used to describe the number and type of elements that constitute a compound

It is a process in which the original substances are changed to one or more new substances.

H HO

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Formation of CompoundsChemical combination of elementsMagnesium and oxygen combine chemically to produce magnesium oxide (compound)

Word equation : Magnesium + oxygen magnesium oxide (element

)(element)

(compound)

Chemical combination of elements and compoundsWhen colourless oxygen and nitrogen dioxide is mixed, they combine chemically to produce a coloured compound, nitrogen dioxide

Word equation : Nitrogen oxide + oxygen nitrogen dioxide (compoun

d)(element)

(compound)

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Chemical combination of compounds

When colourlesscolourless gaseous ammonia is mixed with colourless gaseous hydrogen chloride, they combine chemically to produce a white solid, ammonium chloride.

Word equation : Ammonia + hydrogen chloride ammonium chloride (compoun

d)(compound)

(compound)

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6.4 Some Common Characteristics of Compounds

All compounds share some common properties which enable us to identify them.

• Compounds are formed by chemical reactions, which usually involve an exchange of energy (heat/light) with the surroundings.

• A compound has properties that are different from the properties of its constituent elements

Sodium (solid)

Chlorine (gas)

Sodium chloride (solid)

+

How is sodium chloride different from sodium or chlorine?

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• A compound can only be broken down into simpler substances by chemical methods (e.g. thermal decomposition)

• The different elements in a compound are chemically combined in a fixed proportion by mass

2g of hydrogen + 4g of oxygen 6g of water

boiling to dryness

evaporating dishpipe clay triangletripod stand

Bunsen burner

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6.5 Mixtures

A mixture is made up of two or more substances not chemically combined.It may consist of elements, compounds or both.

It may be made up by solids, liquids or gases.

Examples of Useful Mixtures:

Clean airIt is a mixture of gaseous

elements (nitrogen, oxygen) and compounds (carbon dioxide)

Duralumin

It is a mixture of aluminium, copper, magnesium and manganese

Other examples of mixtures include fog, muddy water, honey, milk, some medicines, brass and steel.

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6.6 Some Common Characteristics of Mixtures

Mixtures• Not formed by chemical reactions (no heat/light energy is given out or taken in)• has properties of its constituent substance

• Substances can be mixed in any proportion by mass• It can be separated into its components by physical means (evaporation, filtration, distillation)

evaporating dishpipe clay triangletripod stand

Bunsen burner

cooling water out

cooling water in distillate

The solution is heated

heat

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6.7 Distinguishing Among Elements, Compounds and MixturesWith the help of classification keys, it is easier to differentiate elements, compounds and mixtures.

Some examples of classification keys

Branching out every section under elements, compounds and mixtures makes comparing them so much easier, now even I can differentiate them fast!

Classification web

Classification branch