1. Elements, Compounds and Mixtures
CHAPTER 4
Elements, Compounds and Mixtures
© 2013 Marshall Cavendish International (Singapore) Private Limited

2. Elements, Compounds and Mixtures
Chapter 4
Elements, Compounds and Mixtures
4.1 Elements
4.2 Compounds
4.3 Mixtures

3. 4.1 Elements Learning Outcomes
At the end of this section, you should be able to:
define an element;
state the chemical symbols for a number of elements. 3

4. Examples: Carbon, copper, oxygen
4.1 Elements
What is an Element?
It is a pure substance that cannot be broken down into two or more simpler substances by chemical processes.
Examples: Carbon, copper, oxygen
Sugar is not an element.
When heated, it breaks down into carbon and water vapour.
Teacher should elicit responses from students as to what they think are elements.
Examples such as sugar and water (shown in the next slide) are given to show that these can be split into other simpler substances when heated or electrolysed.

5. 4.1 Elements Is Water an Element? Water is not an element.
It can be broken down into hydrogen and oxygen.
Hydrogen and oxygen are elements.
To point out that not only does water break down into simpler substances by electrolysis but that these substances, hydrogen and oxygen, are elements.
Clicking the URL will lead to which is a simple experiment explaining the electrolysis of water to form hydrogen and oxygen gas. It is also important for the students to understand the ratio between hydrogen and oxygen gas. Video duration is 1.39 mins.
URL

6. Chemical Symbols of Elements
Chemists use chemical symbols to represent elements.
Each symbol is unique, consisting of one or two letters.
Element
Symbol
calcium Ca
carbon C
hydrogen H
iron Fe
Element
Symbol
mercury Hg
neon Ne
silicon Si
sodium Na
The table shows a few examples of elements. Teachers should point out that the first letter of a symbol is always capitalised and if followed by a second letter, then the second letter should be in lower case.
The names and symbols of all known elements are found in Periodic Table. 6

7. 4.1 Elements
Using the Periodic Table, find the symbols of the following elements.
Element
Symbol
Aluminium
Magnesium
Lead
Copper
Nitrogen
Neon
Bromine
Sulfur Al Mg Pb Cu N Ne Br S 7

8. 4.1 Elements Classification of Elements
Based on their properties, elements are classified into:
metals; e.g. sodium, magnesium, calcium
non-metals; e.g. hydrogen, carbon, chlorine
metalloids. e.g. boron, silicon, germanium, arsenic
(Metalloids have properties of metals and non-metals.) 8

9. 4.1 Elements Differences Between Metals and Non-Metals Properties
Metalloids
Non-metals
Appearance
Shiny (lustrous)
Dull (non-lustrous)
Physical state at r.t.p.
Mostly solids (except mercury)
Solids
Gases, volatile liquids or solids
Melting and boiling points
High (except for sodium, potassium and mercury)
High
Low (except for carbon and silicon)
Heat and Electrical Conductivity
Good
Moderate
Poor (except carbon in the form of graphite and diamond) 9

10. 4.1 Elements Differences Between Metals and Non-Metals Properties
Metalloids
Non-metals
Ductility and Malleability
 Ductile (can be drawn into wires)
 Malleable (can be hammered into different shapes without breaking
 Sonorous (makes a ringing sound when struck)
Brittle (easily broken when hammered)
Brittle if solid 10

11. 4.1 Elements Atoms and Molecules
An element is made up of tiny particles called atoms.
Atoms are the smallest particles of an element that have the chemical properties of that element.
The atoms of an element are different from that of another element.
neon atom
gold atom
The two examples in this slide should be used to explain that all gold atoms are similar, as are neon atoms. However, the atoms of gold are not similar to the atoms of neon.

12. 4.1 Elements Atoms and Molecules
A molecule is a group of two or more atoms that are chemically combined (joined together).
Elements like hydrogen, oxygen, ozone and sulfur exist as molecules.
Diatomic molecules are those that are formed by the combination of two atoms.
E.g. hydrogen, oxygen, nitrogen.
To emphasise that although hydrogen, oxygen and nitrogen exists as diatomic molecules, the hydrogen atom, nitrogen atom and oxygen atom are all different from each other.

13. 4.1 Elements Polyatomic Molecules
Polyatomic molecules consists of three or more atoms that are chemically combined together.
phosphorus (P4)
ozone (O3)
sulfur (S8)

14. Elements, Compounds and Mixtures
Chapter 4
Elements, Compounds and Mixtures
4.1 Elements
4.2 Compounds
4.3 Mixtures

15. 4.2 Compounds Learning Outcomes
At the end of this section, you should be able to:
define a compound;
describe the difference between elements and compounds;
deduce the formula of a compound from the ratio of elements present. 15

16. 4.2 Compounds What is a Compound? What are compounds made of?
A compound is a pure substance that contains two or more elements that are chemically combined in a fixed ratio.
What are compounds made of?
sodium ion
chloride ion
water molecule
molecules
ions 16

17. Properties of Compounds
A compound has different properties from the elements that form it.
Example:
When magnesium is burned, it combines with oxygen in the air to form a compound called magnesium oxide.
magnesium oxygen  magnesium oxide
shiny grey solid colourless gas white solid
Clicking on the URL button will link you to < a website with a video on combustion of magnesium. (The video is approximately 1.3 minutes long.)
URL 17

18. calcium carbonate (marble)
4.2 Compounds
Names of Compounds
Each compound has a chemical name indicating the elements it contains.
Compound
Elements present
sodium chloride
sodium, chlorine
carbon dioxide
carbon, oxygen
zinc oxide
zinc, oxygen
calcium carbonate (marble)
calcium, carbon, oxygen
copper(II) sulfate
copper, sulfur, oxygen
hydrogen chloride
hydrogen, chlorine

19. Chemical formula for lead(II) nitrate
4.2 Compounds
Chemical Formula
A compound can be represented by a chemical formula.
The chemical formula shows:
the types of elements present;
the ratio of the different atoms present.
Chemical formula for lead(II) nitrate
Pb(NO3)2 Pb
1 lead atom
(N)2
1 × 2 =
2 nitrogen atoms
(O3)2
3 × 2 =
6 oxygen atoms

20. Composition of Compounds
Every compound has fixed compositions of the different elements it contains.
Chemical formula can be deduced by the ratio of atoms present in a compound.
Compound
Chemical formula
Ratio of atoms
hydrogen chloride
HCl
H : Cl = 1 : 1
carbon dioxide
CO2
C : O = 1 : 2
carbon monoxide CO
C : O = 1 : 1
sulfuric acid
H2SO4
H : S : O = 2 : 1 : 4
sulfurous acid
H2SO3
H : S : O = 2 : 1 : 3
ethanol
C2H5OH
C : H : O = 2 : 6 : 1 20

21. Decomposition of Compounds
A chemical reaction is necessary to separate the elements in a compound.
In thermal decomposition, heat is used to break down compounds into elements or simpler compounds.
mercury(II) oxide
mercury
oxygen gas
To point out that it is not simply ‘heat’ or ‘electricity’ that is used to separate a compound into simpler substances, but that these are means of providing large amounts of energy for separation to take place.
Electrolysis will be covered in greater detail in Chapter 15.
Compounds can also be broken down by using electricity.
This process is known as electrolysis. 21

22. Elements, Compounds and Mixtures
Chapter 4
Elements, Compounds and Mixtures
4.1 Elements
4.2 Compounds
4.3 Mixtures

23. 4.3 Mixtures Learning Outcomes
At the end of this section, you should be able to:
define a mixture;
differentiate between compounds and mixtures. 23

24. 4.3 Mixtures What are Mixtures?
Mixtures are made up of two or more substances that are not chemically combined.
Examples of mixtures:
petrol
air
muddy water
alloys such as brass, bronze and steel
Discuss with students what they think are present as components in these mixtures.
Muddy water – sand, soil particles, clay particles and water
Petrol – various hydrocarbons
Air – nitrogen, oxygen, carbon dioxide
Brass – copper and zinc
Bronze – copper and tin
Steel – iron, carbon and other metals 24

25. 4.3 Mixtures Types of Mixtures A mixture can exist as a combination of
two elements;
two compounds;
one element and one compound.

26. Mixture of Two Elements
4.3 Mixtures
Mixture of Two Elements
Example:
Neon and Hydrogen
hydrogen
(H2)
neon
(Ne)
Neon is monatomic.
Hydrogen is diatomic.
This and the following two slides not only show the different types of mixtures but are useful in reinforcing the differences between atoms and molecules, elements and compounds. 26

27. Mixture of Two Compounds
4.3 Mixtures
Mixture of Two Compounds
Example:
Water and Carbon dioxide
water
(H2O)
carbon dioxide
(CO2)
A water molecule is made up of two hydrogen atoms and one oxygen atom.
A carbon dioxide molecule is made up of two oxygen atoms and one carbon atom.

28. Mixture of an Element and a Compound
4.3 Mixtures
Mixture of an Element and a Compound
Example:
Hydrogen and Ammonia
hydrogen
(H2)
ammonia
(NH3)
Hydrogen is an element.
Ammonia is a compound.
Each ammonia molecule consists of three hydrogen atoms and one nitrogen atom.

29. Differences between Mixture and Compound
4.3 Mixtures
Differences between Mixture and Compound
Mixture
Compound
Separation
The components of a mixture can be separated by physical processes such as magnetic separation, filtration or distillation.
A compound can only be broken down into its elements or into simpler compounds by chemical processes (e.g. thermal decomposition or electrolysis).
Properties
The chemical properties of a mixture are the same as those of its components.
The physical and chemical properties of a compound are different from those of its constituent elements.

30. Differences between Mixture and Compound
4.3 Mixtures
Differences between Mixture and Compound
Mixture
Compound
Energy changes
No chemical reaction takes place when a mixture is formed — usually there is little or no energy change.
A chemical reaction takes place when a compound is formed — usually there is an energy change, e.g. the reactants get hot or cold.
Composition
The components of a mixture can be mixed in any proportion.
The elements in a compound are always combined in a fixed proportion.

31. 4.3 Mixtures
Example:
Comparing a mixture of iron filings and sulfur with a compound iron(II) sulfide
Separation
Mixture
Compound
Can be separated by physical methods
E.g. In a mixture of iron filings and sulfur, iron filings can be separated with the use of a magnet.
Can only be separated by chemical methods or by using electricity
E.g. Iron in iron(II) sulfide cannot be simply separated with a magnet. 31

32. Physical and Chemical Properties
4.3 Mixtures
Example:
Comparing a mixture of iron filings and sulfur with a compound iron(II) sulfide
Physical and Chemical Properties
Mixture
Compound
Has the same chemical properties as its components
E.g. In a mixture of iron filings and sulfur, each component retains their colour, texture and magnetic property (iron).
Has different physical and chemical properties from those of its components
E.g. Iron(II) sulfide has a different appearance from iron filings or sulfur; has no magnetic property.
Discuss the colour and texture of iron filings, magnetic property; colour and texture of sulfur.
Sulfur – yellow powder
Iron filings – dark grey powder 32

33. 4.3 Mixtures
Example:
Comparing a mixture of iron filings and sulfur with a compound iron(II) sulfide
Energy Change
Mixture
Compound
No chemical reaction takes place. Little or no energy change.
E.g. Mixture of iron filings and sulfur – no chemical change takes place without heating.
Chemical reaction takes place. Heat and light usually given off.
E.g. When a mixture of iron filings and sulfur is heated, it glows red hot to form
iron(II) sulfide.

34. 4.3 Mixtures
Example:
Comparing a mixture of iron filings and sulfur with a compound iron(II) sulfide
Composition
Mixture
Compound
No fixed composition.
E.g. A mixture of iron filings and sulfur can have more or less of each component.
Fixed composition.
E.g. The compound iron(II) sulfide is formed in the ratio of iron to sulfur (by mass) of 7:4.
The differences between mixtures and compounds can be discussed with reference to a mixture of iron filings and sulfur, and the compound iron(II) sulfide, both of which contain the elements iron and sulfur. 34

35. Elements, Compounds and Mixtures
Chapter 4
Elements, Compounds and Mixtures
Concept Map

36. Elements, Compounds and Mixtures
Chapter 4
Elements, Compounds and Mixtures
The URLs are valid as at 15 October 2013.
Acknowledgements
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