Elements, Compounds and Mixtures.

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Elements, Compounds and Mixtures.

• Chapter 16

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Classification of Substances

• Elements
• Molecules
• Compounds
• Mixtures.

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Elements

• Elements are substances made up of only one type
  of atom.
• Example ? Hydrogen, Gold.

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Periodic Table of Elements
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Molecule

• A molecule is made up of two or more atoms
  chemically combined.

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Compounds

• Compounds are made up of two or more different
  types of atoms chemically combined.

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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.

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• Diagram of Salt, water, sucrose.

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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

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Compare mixtures and Compounds.
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Mixture Compound
The amounts of the substances in the mixture can vary. The elements in a compound are always present in the same fixed proportion.
A mixture contains two or more substances A compound is a single 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 changes when a mixture is made Heat is usually given out or taken in when a compound is formed.
It is usually easy to separate the components of a mixture. It is usually difficult to separate the components of a compound.
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iron particles
Key
one iron particle
strong bonds between iron particles
iron particlesheld together by strong bonds
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iron particles
iron particles are attracted to a magnet
iron particlesdiagram
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sulfur particles
Key
one sulfur particle
strong bonds between sulfur particles
sulfur particles held together by strong bonds
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sulfur particles
sulfur particles are not attracted to a magnet
sulfur particlesdiagram
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iron particles
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A mixture of iron and sulfur particles
Whats this?
strong bonds between sulfur particles
strong bonds betweeniron particles
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A mixture of iron and sulfur particles
A magnet attracts the iron particles
but not the sulfur particles.
The mixture is separated
mixture diagram
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A compound between iron and sulfur particles
Whats this?
one sulfur particle
one iron particle
strong bonds between iron and sulfur particles
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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
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References
Steve Lewis for the Royal Society of
Chemistry Photographs by Peter Hollamby
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A
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B
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C
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D
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E
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F
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G
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H