Elements Compounds and Mixtures

1. Elements,
Compounds
and Mixtures

2. Learning Objectives
• At the end of the lesson, students should
be able to:
– describe the differences between elements,
compounds and mixtures

3. Elements
• Pure substance that cannot be split up into two or more
simpler substances.
• Can be represented using chemical symbols (refer to the
Periodic Table)
• Elements can exist as either atoms or molecules.
• Atoms are the smallest particles of an element that have
the chemical properties of that element.
• Molecules are a group of two or more atoms that are
chemically combined.

4. Properties of Metals and Nonmetals
• Elements can be classified into metals and nonmetals.
• A dividing staircase line separates the metals
from the non-metals in the periodic table.
dividing
line
Figure 1. Periodic table showing metals and
non-metals

5. Properties of Metals and Nonmetals
Metals
Non-metals
shiny appearance
dull appearance
solids at room temperature.
(except mercury)
either gases, volatile liquids or
solids with low melting points at
room temperature. (except carbon)
Malleable, ductile, sonorous
Brittle if solid
High melting and boiling points
Low melting and boiling points
Good conductors of heat
Poor conductors of heat
Good conductors of electricity in
all states of matter
Poor conductors of electricity
(except carbon)
Elements that have properties of both metals and non-metals
e.g. silicon are called metalloids.

6. Wake Up Call 1
1. Which of the following contains three
elements?
A
B
C
D
argon, magnesium, phosphorus
brass, phosphorus, potassium
chlorine, air, nitrogen
petrol, alcohol, water

7. Wake Up Call 1
2. Which of the following is an element?
A
B
C
D
CO
H2
HCl
HI

8. Wake Up Call 1
3. (a) How many types of elements are
there in sulfuric acid, H2SO4?
(b) How many atoms are there in one
molecule of sulfuric acid H2SO4?

9. Compounds and Mixtures
• A compound is a substance that is made
up of two or more elements chemically
combined together.
• A mixture consists of two or more
substances (elements or compounds) that
are not chemically combined together.

10. Compounds and Mixtures
Compound
Mixture
1)
Formation
A chemical reaction
takes place when a
compound is formed,
usually there is an
energy change (e.g.
heat is given off).
No chemical change
takes place when a
mixture is formed,
usually there is little or
no energy change.
2)
Composition
Has fixed composition Has variable
by mass. E.g. H2O – 2 composition by mass.
units of hydrogen, 1
unit of oxygen
3)
Melting and
Boiling point
Has fixed melting and
boiling points.
Has variable melting
and boiling points
(melt and boil over a
range of
temperatures)

11. Compounds and Mixtures
Compound
Mixture
4)
Properties
Has its own physical
and chemical properties
which are different
from its elements – i.e.
hydrogen and oxygen
are gases at rtp, water is
a liquid at rtp.
Does not have its own
properties, it has the
same properties as its
components
5)
Separation
The constituents
(elements) can only be
separated by chemical
methods.
The constituents can be
separated from one
another by physical
methods.
6)
Arrangement
of atoms
A compound of 2 elements
A mixture of 2 elements

12. Wake Up Call 2
1. Classify the following substance as an element, a
compound or a mixture.
Substance
H2O
Copper (Cu)
Steel
Ice (H2O)
O2
C2H5OH
Carbon
Brass
NO2
Air
Seawater
Element, compound or mixture?

13. Comparing Elements, Compounds
and Mixtures
Elements
% composition by
mass
Atoms
Heating /
combustion
Can be separated
by physical
means?
Appearance
Compounds
Mixtures
Fixed/constant
Fixed/constant
Variable
One type
Two or more
different types
Two or more
different types
Only one product
formed or oxidises
to one other
substance
May have two or
more products
formed /
decomposes
May have two or
more products
formed
No
No
Yes
Only one colour
Only one colour
Can be two or
more colours

14. Comparing Elements, Compounds
and Mixtures
Elements
Some parts
dissolve in water
and some parts
do not
Examples
Pure / Impure
Compounds
Mixtures
Not possible
Not possible
Possible
Metals, Na, Ca,
Ar, Ne, H2, Cl2,
O3, P4, S8
HCl, CO2, H2O.
Na2SO4
Crude oil
(petroleum),
alloys (brass,
steel, bronze), air,
solutions,
fractions from
crude oil (diesel,
petrol, bitumen)
Pure
Pure
impure