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Chapter 3
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E
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Water evaporation, cutting a
paper…

Chemical Change: A new substance is made and the change isn’t easily
reversed
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g
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Like heating up the water
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It’s made of identical atoms
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Mixture: It’s formed when elements or compounds do not react
together
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If we can’t, we say it is homogeneous
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They have high
melting points
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Malleable
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Sonorous
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Low melting
points
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Brittle
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E
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Water
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E
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Sand
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Concentration: The relationship that exists between the amount of
solute and the amount of solvent
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Atoms are made of subatomic particles
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Sub-atomic particle
Proton
Neutron
Electron

Relative mass
1
1
About 1
1836

Relative charge
+1
0
-1

Protons and neutrons are found in the centre of an atom, in the nucleus
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The number of
protons and electrons are the same as the number of positive charge must
be equal to the negative charge
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They are completely
stable as they have 8 electrons in their outer shell
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Nucleon Number or
mass number:
The number of protons +
electrons
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Proton Number or atomic
number:
The number of protons which
equals the number of electrons
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As the chemical
properties of an element depend on the number of electrons in the outer
electron shell
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Formation of ions: Ionic compounds contain a metal combined with
one or more non-metals
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Ions are formed from atoms by the gain or loss of
electrons
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Ionic bonds: This form when 2 or more atoms bond to get a full outer
shell
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Ionic bonds happen between metals
and non-metals
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They can share 1, 2 or 3
electrons
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Covalent bonds: They form when atoms of non-metals combine
together, and become simple molecules
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This
electron pair are known as bonding pairs
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Practice examples of dot and cross diagrams of covalent bonds
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They dissolve in water and aren’t volatile
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They are completely
volatile as they evaporate easily and have very low electrical conductivity,
because they don’t contain ions
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While covalent compounds have a low melting
point and boiling point as the intermolecular forces of attraction between
molecules are weak
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These different forms of an element are called allotropes
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The diamond is very strong
substance, as each carbon atom is covalently bonded to 4 others
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This is because it has weak forces of attraction between the
layers in graphite
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Diamonds are
used for cutting, as they are so strong
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Silicon: Silicon (IV) oxide has a macromolecular structure
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Every silicon atom has 4 covalent bonds,
that why it has high boiling and melting points and is hard like diamond
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However, is not as strong as the
diamond because is made by different elements oxygen and silicon

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