Elements, Compounds and
Mixtures.
Chapter 16
Classification of Substances
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Elements
Molecules
Compounds
Mixtures.
Elements
• Elements are
substances
made up of
only one type
of atom.
• Example 
Hydrogen,
Gold.
Periodic Table of Elements
Molecule
• A molecule is
made up of two
or more atoms
chemically
combined.
Compounds
• Compounds are made up of two or more
different types of atoms chemically
combined.
Properties of Compounds
• When a compound is formed during a
chemical reaction its properties differ from
those of the elements from which it is made.
• Example: Water is made from hydrogen
and oxygen.
Hydrogen  flammable gas
Oxygen  colourless gas.
• Diagram of Salt, water, sucrose.
Mixtures
• A mixture consists of two or more different
substances mingled together but not
chemically combined.
• Examples:
Sea – water and salt
Air – nitrogen, oxygen …
Soil – sand, clay, humus …
Compare
mixtures and
Compounds.
Mixture
The amounts of the substances
in the mixture can vary.
Compound
The elements in a compound are
always present in the same fixed
proportion.
A mixture contains two or more A compound is a single
substances
substance.
The properties of a mixture are
similar to those of the
substances in a mixture.
The properties of a compound
are different to those of the
elements which reacted to form
it.
There are practically no energy Heat is usually given out or
changes when a mixture is made taken in when a compound is
formed.
It is usually easy to separate the It is usually difficult to separate
components of a mixture.
the components of a compound.
iron particles
Key:
one iron particle
strong bonds
between iron particles
iron particles
held together
by strong bonds
iron particles
iron particles are attracted
to a magnet
iron particles
diagram
sulfur particles
Key:
one sulfur particle
strong bonds between sulfur
particles
sulfur particles
held together
by strong bonds
sulfur particles
sulfur particles are not attracted
to a magnet
sulfur particles
diagram
iron
particles
sulfur particles
What’s this?
A mixture
of iron and sulfur particles
strong bonds
between
iron particles
strong bonds between
sulfur particles
A mixture
of iron and sulfur particles
A magnet attracts the
iron particles
but not the
sulfur particles.
The mixture is separated
mixture diagram
What’s this?
A compound between
iron and sulfur particles
one iron particle
one sulfur particle
strong bonds between
iron and sulfur particles
A compound between
iron and sulfur particles
strong bonds
between
iron and sulfur
particles
The magnet cannot
separate iron and sulfur
particles in a compound
compound diagram
References
Steve Lewis for the Royal Society of Chemistry
Photographs by Peter Hollamby
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