An element is a substance which cannot be split into two or more simpler substances by chemical processes or by electricity
Elements can be classified into metals, non-metals and metalloids (elements that have properties of both metals and non-metals, eg. silicon)
Physical properties of metals and non metals
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Metals
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Non-metals
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- Shiny appearance (lustrous)
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- Dull appearance is solid (non-lustrous)
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- Solids at r.t.p (except for mercury)
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- Either gases, volatile liquids or
solids with low melting points at r.t.p (except for carbon)
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- Malleable (can be hammered into
different shapes without breaking)
- Sonorous (make a ringing sound when
struck)
- Ductile (can be drawn into wires)
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- Brittle of solid (easily broken when
hammered)
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- High melting points and boiling points
(except for sodium, potassium and mercury)
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- Low melting points and boiling points
(except for carbon and silicon)
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- Good conductors of heat
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- Poor conductors of heat (except carbon
in the form of diamond and graphite)
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- Good conductor of electricity in all states
of matter
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- Poor conductors of electricity (except
carbon in the form of graphite)
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Definition of a Compound:
A compound is a substance made up of two or more elements chemically combined together.
Definition of a Mixture:
A mixture consists of two or more substances which are not joined together chemically.
Definition of Ions:
An ion is a charged particle formed from an atom or a group of atoms by the loss or gain of electrons
Definition of Atoms:
Atoms are the smallest particles of an element that have the chemical properties of that element.
Definition of Molecules:
A molecule is a group of two or more atoms that are chemically combined/ joined together.
Diatomic: A combination of 2 atoms
eg. O2
Triatomic: Molecules consisting of 3 atoms
eg. O3
Polyatomic: A combination of 4 or more atoms
eg. Sp
Monatomic: Made up of one atom.
eg. He, Ar
Differences between a mixture and a compound
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Mixture
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Compound
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Separation
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The components of a mixture can be
separated by physical methods, eg. filtration, distillation or chromatography
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The elements in a compound can only be
separated by chemical reactions or by using electricity
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Properties
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The chemical properties of a mixture are
the same as those of its components
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The physical and chemical properties of a
compound are different from those of the elements in the compound
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Energy change
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No chemical reaction takes place when a
mixture is formed- usually there is little or no energy change
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A chemical reaction takes place when a
compound is formed- usually there is an energy change, eg. The reactants
become hot
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Composition
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The components of a mixture can be mixed
in any proportion
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The elements in a compound are always
combined in a fixed proportion (by mass)
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Definition of an Alloy:
An alloy is an example of a mixture
An alloy is a mixture of of metals with other elements (usually metals but sometimes non-metals like carbon)
Alloys are widely used and in great demand as they tend to be stronger than pure metals
