Chemistry GCSe Revision

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  • Created on: 31-12-13 17:24
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Atomic Number and Mass
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 of the same element all have the same
number of protons so atoms of different elements will
have a different number of protons
In order to get the neutrons, all we need to do is
subtract the atomic number from the mass number.

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Electrons are not counted in the mmass number
because their relative mass is very small
Compounds are Chemically
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 compounds are formed from a chemical
reaction it is very hard to separate the two original
elements out again.…read more

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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 because of the attraction of opposite charges
"+" and ""
Atoms on the left side of the periodic table have just
one or two electrons in their outer shell,( highest energy
level)..…read more

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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 gives up its outer electron to
chlorine, and so it becomes an Na+ ion
Because the chlorine atom picked up the spare electron
from sodium it becomes a Cl ion causing the two atoms
to stick together due to their opposite charges
Ionic compounds ALWAYS have GIANT IONIC
The ions form a closely packed regular lattice…read more

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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
and electric current, after they are melted
However Ionic compounds dissolve easily in
water.…read more

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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
For example Group 7 elements ( the halogens)
form ionic compounds with alkali metals where
the halide ion has a 1 charge. EG.…read more

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Another example of using the charges present to work
out the formula of an ionic compound is Magnesium
Magnesium Chloride contains Mg2(+2) and Cl (1)
Because chloride only has a 1 charge we need to of
them to balance out the 2+ charge of the magnesium
ion.…read more

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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
Sometimes atoms prefer to make covalent bonds by
sharing electrons with other atoms
They only share electrons in their outer shells
This way BOTH atoms feel that they have a full outer
shell.…read more

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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
Water H20 Oxygen atoms have six outer
electrons. They sometimes form ionic bonds by
taking two electrons to complete their outer shell.…read more

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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..…read more


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