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Chemistry
GCSe
Revision



Atomic Number and Mass
Number
The mass number at the top of the element indicates
the total number of protons and neutrons
The atomic number at the bottom of the element
indicates the number of protons.
The atomic number tells us how many protons there
are, atoms…

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Electrons are not counted in the mmass number
because their relative mass is very small

Compounds are Chemically
Bonded
Compounds are formed when atoms of two or more
elements are chemically combined together. For
example Carbon Dioxide is a compound formed from a
chemical reaction between Carbon and Oxygen.
Because…

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Carbon12 has 6 protons, 6 electrons and 6 neutrons.
Carbon 14 has 6 Protons, 6 electrons and 8 neutrons

Ionic Bonding
When Ionic bonding occurs, atoms lose or gain
electrons in order to form charged particles also known
as ions , these "ions" are then strongly attracted to one
another…

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nearly full, these elements are pretty eager to gain that
one or two electrons in order to fill that outer shell up.
When this process happens they become ions and
before you know it they are latched onto another atom (
ion ) with an opposite charge
For example Sodium…

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High melting points and high boiling points due
to the strong attraction between the ions
It takes a lot of energy to overcome this
attraction, however when the ionic compounds
finally do melt , the ions are free to move. Due to
the delocalised electrons, ions are able to carry…

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For example Group 1 elements form ionic
compounds with non metals where the metal ion
has a 1+ charge . EG. K+Cl
Group 6 & 7 elements are NON METALS and
therefore gain electrons in order to form negative
ions
For example Group 7 elements ( the halogens)
form ionic…

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each ion so the formula for sodium chloride becomes
NaCl
Another example of using the charges present to work
out the formula of an ionic compound is Magnesium
Chloride
Magnesium Chloride contains Mg2(+2) and Cl (1)
Because chloride only has a 1 charge we need to of
them to balance…

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Some elements bond ionically however some form
strong covalent bonds. This is where atoms share
electrons with each other in order to have a full outer
shells
Sometimes atoms prefer to make covalent bonds by
sharing electrons with other atoms
They only share electrons in their outer shells
This way…

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Hydrogen Chloride HCl ­ very similar to H2 and
CL2, both atoms only need one more electron in
order to complete their outer shells
Ammonia NH3 nitrogen has five outer electrons,
because of this it needs to form 3 covalent bonds
to make up for the extra three electrons needed…

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However the forces of attraction between the
molecules are very weak
Because of these weak intermolecular forces, the
melting and boiling points of simple molecular
substances are very low and so the molecules
are easily broken..
**** IT IS THE INTERMOLECULAR FORCES
THAT GET BROKEN WHEN SIMPLE
MOLECULAR SUBSTANCES MELT…

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