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Metals and Non-metalsMetallic
elements occupy the
left side and middle
of the
periodic table. Non-metals
are found on the
right
side of the periodic table. Testing for metals and non-metals: • metals conduct electricity; non metals do not conduct electricity – except graphite !• oxides of
metals
form
alkaline
solutions in water
non-metals
form
acidic
solutions in water
Experiments to show that magnesium is a metal:• electrical conductivity test:
conducts electricity
- burning to form magnesium oxide, dissolvingmagnesium oxide in water, and testing pH:
alkaline
solution
2Mg
(s)^
+ O
2(g)
2MgO
(s)
Experiments to show that sulphur is a non-metal:• electrical conductivity test:
does not conduct
- burning to form sulphur dioxide, dissolving sulphurdioxide in water, and testing pH:
acidic solution
S^ (s)
+ O
2(g)
SO
2(g)
Chemical Families Elements in the same Group have the same number of outer shell electrons. The
same
number of outer shell electrons
means
similar chemical properties
chemical family.
Group 1 – The Alkali Metals
Group 7 – The Halogens
Group 0 – The Noble Gases
Comparing Group 1 metals to typical metals
Trends Going down Group 1 the metals
softer
more dense
-^ melt
and
boil
at
lower
temperatures
Chemical Properties of alkali metals Group 1 metals are very reactive! They are normally stored under oil. The oil acts as abarrier preventing them from reacting with oxygen in the air, or with water.
An alkali metalin water
An alkali metalstored in oil
Trend Reactivity
increases
as
we go
down
the group
Explaining the order of reactivity in Group 1 Group 1 elements react by losing their outer shell electron to form metal ions with a 1+charge, and hence gain a full outer shell.The further away from the positively charged nucleus the outer shell electron is, the easier itis for the atom to lose it, so the more reactive the element is.This is because the attraction between the negatively charged electron and the nucleus getsweaker the further away the electron is, and the more shells there are in between.
Group 7 - The Halogens The Halogens are the elements in Group 7They are
non-metals,
having
coloured vapours
The halogen elements consist of molecules made up of
pairs
of atoms. e.g. chlorine is Cl
2(g)
They each have 7 electrons in their outer shell
Trends in the physical propertiesof the halogens As we go down Group 7:
•^
colour increases in intensity
-^
state goes from gas to liquid to solid
-^
melting point increases
-^
boiling point increases
We would therefore predict that
astatine
would be a very dark (black) element, solidat room temperature, and with a meltingand boiling point higher than those of iodine.
Trend in reactivity
Reactivity of the halogens
decreases
as we go
down
the group (opposite trend to Group 1)
Chemical Properties The halogens have 7 electrons in their outer shell. They react by gaining an electron tocomplete their outer shell, or by sharing electrons with other atoms.Reactions with metalsWhen a halogen atom
gains an electron
it forms an
ion with
a 1- charge
, which we call a halide ion: fluoride
- F
chloride
Cl
bromide Br
iodide
- I
(see notes on reactions of Group 1metals with halogens)
Reactions with non-metalsHalogens can react with other non-metals, sharing their outer shell electrons to formbonds.
e.g.
H2(g)
+^
Cl
2(g)
2HCl
(g)
hydrogen + chlorine
hydrogen chloride
Group 8 or 0 - The Noble Gases The noble gases are in Group 8 (aka Group 0)They are all
colourless gases
They are very
unreactive
They exist as
individual atoms
rather than forming molecules.
Uses - balloons:Helium
is used (rather than hydrogen) in lighter-than-air
balloons because its lack of reactivity means it will notignite. The only other gas with a sufficiently low density ishydrogen, which is extremely flammable and dangerous. Uses – in discharge tubes: When electricity is passed through a glass tube containing anoble gas at low pressure, the atoms are excited and light isproduced. Each noble gas produces a different colour. Neon
is the brightest, hence its use in advertising signs.
Uses – inert atmospheres:Argon
is used to fill light bulbs because it
is very unreactive. It prevents thetungsten filament from reacting withoxygen when it gets hot, and “burningout”. It is also used when welding toprevent oxygen getting to the hot metaland causing corrosion.
Explaining the lack of reactivity Their lack of reactivity is because they have a
full outer shell
and
therefore
don’t form stable ions
It takes a lot of energy to rearrange the full outer shell so as to beable to form bonds with other elements to form a molecule, sothis doesn’t happen either.
Ar
