elements, compounds and mixtures. chapter 16. classification of substances elements molecules...
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Elements, Compounds and Mixtures.
Chapter 16
Classification of Substances
• 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 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.
iron particlesKey:
strong bonds between iron particles
one iron particle
iron particlesheld together by strong bonds
iron particles
iron particles are attracted to a magnet
iron particlesdiagram
sulfur particlesKey:
strong bonds between sulfur particles
one sulfur particle
sulfur particles held together by strong bonds
sulfur particles
sulfur particles are not attracted to a magnet
sulfur particlesdiagram
iron particles
sulfur particles
A mixture of iron and sulfur particles
strong bonds between sulfur particles
strong bonds betweeniron particles
What’s this?
A mixture of iron and sulfur particles
A magnet attracts the iron particles
but not the sulfur particles.
The mixture is separated
mixture diagram
one sulfur particle one iron particle
strong bonds between iron and sulfur particles
What’s this?A compound between iron and sulfur particles
strong bonds between iron and sulfur particles
A compound between iron and sulfur particles
The magnet cannot separate iron and sulfur particles in a compound
compound diagram
ReferencesSteve Lewis for the Royal Society of Chemistry
Photographs by Peter Hollamby
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