UNIT 2 - PROPERTIES OF MATERIALS.
Periodic table
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Elements are arranged on the Periodic Table in order of increasing atomic
number, where each element has one proton more than the element preceding it
The table is arranged in vertical columns called Groups numbered I - VIII
(numbers shown on the course's Periodic Table) and in rows
called Periods (numbers not shown on the Periodic Table)
Period: these are the horizontal rows that show the number of shells of electrons
an atom has
o Eg. elements in Period 2 have two electron shells, elements in Period 3
have three electron shells
Group: these are the vertical columns that show how many outer electrons each
atom has
o Eg. Group 4/ IV elements have atoms with 4 electrons in the outermost
shell, Group 6 elements have atoms with 6 electrons in the outermost
shell
All elements are arranged in the order of increasing atomic number from left to
right
Predicting properties using the Periodic table
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Because there are patterns in the way the elements are arranged on the
Periodic table, there are also patterns and trends in the chemical behaviour of
the elements and their physical properties
There are trends in properties down Groups and across each Period
All the Group I elements, for example, react very quickly with water
In this way the Periodic Table can be used to predict how a particular element
will behave
The Periodic Table can also be used to predict boiling point, melting point,
density and many more properties by comparing to nearby elements.
IMPORTANT ‘ GROUPS ‘
Group I Properties & Trends
Electronic configuration and reactivity in Group I
Diagram showing electronic configuration of the first three elements in Group I
Explaining the trend in reactivity in Group I
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The reactivity of the Group 1 metals increases as you go down the group
Each outer shell contains only one electron so when they react, they lose the
outer electron which empties the outermost shell
The next shell down automatically becomes the outermost shell and is already
full, hence the atom obtains an electronic configuration which has a full outer
shell of electrons and is stable
As you go down Group 1, the number of inner complete shells of electrons
increases by 1 per row (period number increases down the Periodic Table)
This means that the outer electron is further away from the nucleus so there
are weaker electrostatic forces of attraction
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This requires less energy to overcome the electrostatic forces of attraction
between the negatively charged electron and the positively charged nucleus
This allows the electron to be lost more easily, making the Group I metal atoms
more reactive as you go down the group
Group VII Properties & Trends
The halogens
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These are the Group VII non-metals that are poisonous and include fluorine,
chlorine, bromine, iodine and astatine
Halogens are diatomic, meaning they form molecules of two atoms
All halogens have seven electrons in their outer shell
They form halide ions by gaining one more electron to complete their outer shells
Fluorine is not allowed in schools, so observations and experiments tend to only
involve chlorine, bromine and iodine
The Appearance, Characteristics and Colour in Solution of the Halogens
Properties of the halogens
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At room temperature (20 °C), the physical state of the halogens changes as you
go down the group
Chlorine are a pale yellow-green gas, bromine is a red-brown liquid and iodine
is a grey-black solid
This demonstrates that the density of the halogens increase as you go down
the group:
The physical state of the halogens at room temperature
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Reactivity of Group VII non-metals increases as you go up the group (this is the
opposite trend to that of Group I)
Each outer shell contains seven electrons and when the halogen reacts, it will
need to gain one outer electron to get a full outer shell of electrons
As you go up Group VII, the number of shells of electrons decreases (period
number decreases moving up the Periodic Table)
This means that the outer electrons are closer to the nucleus so there
are stronger electrostatic forces of attraction, which help to attract the extra
electron needed
This allows an electron to be attracted more readily, so the higher up the
element is in Group VII then the more reactive it is
Diagram showing the electronic configuration of the first three elements in Group
VII
Reaction of the halogens with halide ions in displacement reactions
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A halogen displacement reaction occurs when a more reactive halogen
displaces a less reactive halogen from an aqueous solution of its halide
The reactivity of Group VII non-metals increases as you move up the group
Out of the three commonly used halogens, chlorine, bromine and iodine, chlorine
is the most reactive and iodine is the least reactive
Aqueous solution colour of halogens
The Noble Gases
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The noble gases are in Group VIII (or Group 0); they are non-metals and
have very low melting and boiling points
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They are all monoatomic, colourless gases
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The Group 0 elements all have full outer shells of electrons
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This electronic configuration is extremely stable so these elements are
unreactive and are inert
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Electronic configurations of the noble gases:
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He: 2
Ne: 2,8
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Ar: 2,8,8
Kr: 2,8,18,8
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Xe: 2,8,18,18,8
Noble gases are inert (unreactive) as they have a full outer shell of electrons so
do not easily loss or gain electrons
Uses of the Noble Gases
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Helium is used for filling balloons and weather balloons as it is less
dense than air and does not burn
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Neon, argon and xenon are used in advertising signs
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Argon is used to provide an inert atmosphere for welding
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Argon is also used to fill electric light bulbs as it is inert
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Neon and argon are used as inert atmospheres for sensitive
experiments where nitrogen is not appropriate