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Chapter 6:
Elements, Compounds and Mixtures
Before we move on,
We have…
Representing the video clip available
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
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
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???
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
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
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?
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
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
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)
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)
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?
• 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
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.
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
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