Zusammenfassung der Ressource
C4 - Predicting and Identifying
Reactions and Products
- Group 1 - alkali
metals
- One outer shell
electron
- Similar physical properties
- Low melting/boiling
points relatively
- Low density (Li, Na
and K float in water)
- Very soft (can
be cut with a
knife)
- Form ionic compunds
- Very reactive
- readily lose their
single outer shell
electron
- Form a 1+ ion
- As you move
down group 1,
the metals
become more
reactive
- Outer electron more easily
lost as it's further away
form the nucleus so is less
reactive
- reacts with water
- Metal + water => metal hydroxide + hydrogen
- 2Na + 2H20 => 2NaOH + H2
- React vigorously
in water
- As reactivity increases,
the metals react
differently
- Lithium moves
around and fizzes
furiously
- Sodium and
potassium also fizz
like lithium but they
melt in the heat of
the reaction
- Rubidium and
Caesium react
violently and tend to
explode
- Can also react with
dilute acids
- produces a salt and
hydrogen gas
- 2Na + 2HCl => 2NaCl + H2
- More violent than
reacting with water so
can be dangerous
- Group 7 - halogens
- 7 electrons in the
outer shell
- Exist as diatomic molecules
- Exist as Cl2 or Br2
- Covalently bonded
- Melting/boiling points INCREASE
as you go down the group
- Chlorine is a fairly
reactive poisinous
green gas
- poisonous red-brown liquid,
gives off an orange vapour
- Iodine is a dark grey
crystalline solid which
gives of a purple
vapour when heated
- Reactivity decreases
going down the group
- Only needs to gain one
electron to form a 1- ion
- The easier it is to attract
the electron, the more
reactive the halogen will be
- it's harder to attract an
electron as it's further away
from the nucleus as the
atomic radius grows
- React with alkali metals to form salts
- Sodium + chlorine => sodium chloride
- 2Na + Cl2 => 2NaCl
- alkali metal + halide => metal halide
- Halogens undergo
displacement reactions
- a more reactive halogen
can displace a less reactive
one from a salt solution
- If you add chlorine water to potassium
bromide solution, the chlorine will
displace the bromine from the solution
- Cl2 + 2KBr => Br2 + 2KCl
- These show the
reactivity trends
of the halogens
- measure the halide
salt solution into a
testube
- add a few drops
of the halide
solution and
gently mix
- a colour
change
indicates a
reaction has
happened
- Group 0 - noble gases
- All Group 0 elements are INERT
- They don't really react at all. They
have a full outer shell of electrons
meaning they don't easily give up
or gain electrons
- They are not flammible
- These properties
means it's difficult
to observe them,
they took a long
while to be
discovered
- There are
patterns in
properties
- boiling/melting
point and
density increase
as you move
down the group
- You can estimate
values of elements:
- He (0.2kg/m^3) and Ar
(1.8kg/m^3) means Ne is in
the middle so 0.1kg/m^3
- Transition metals
- "Everyday"
metals, eg
copper,
iron, gold...
- Have
typical
metallic
properties
- Hard, strong, shiny
materials that
conduct heat and
electricity very well
- HIgh melting
points (apart
from mercury)
- Make good catalysts
- Iron is used in the
Haber process
(ammonia)
- Vanadium pentoxide
(V2O5) is used in the
contact process
(H2SO4)
- Can have multiple ions
- Fe2+ and Fe3+
- Cu+ and Cu2+
- Cr2+ and Cr3+
- Colourful compounds
- the colour depends on the
transition metal they
contain
- Fe2+ is usually light green
- Fe3+ is usually orange/brown (rust)
- Cu2+ is usually blue
- Transition metals are fairly
unreactive
- Much less reactive
than group 1 and 2
metals
- Most react with dilute
acids to form metal
salts but they happen
much slower than g1 or
g2 metals
- Reactivity of metals
- How metals react with
acid can tell you about
their reactivity
- place pieces of various
metals in HCl. The more
reactive, the faster the
reaction will happen
- reactive metals will fizz
vigorously, whereas
less reactive metals
might bubble a bit
- You can show that
hydrogen is formed by
using the burnt split test
- Metals can react with water
- metal + water => metal hydroxide + hydrogen
- A reactivity series shows how
reactive metals are
- For example it will show
that Potassium is more
reactive than Magnesium
- More reactive
metals displace
less reactive ones
- if you put an iron nail into
a solution of copper
sulfate, the more reactive
iron displaces the copper
- CuSO4 + Fe => FeSO4 + Cu
- if you put a less reactive metal
into a solution of a more reactive
metal salt, nothing will happen
- You can use
displacement
reactions to work out
a reactivity series
- Test for gases
- Oxygen
- The gas will relight
a glowing splint
- This is because
combustion only happens
when oxygen is present so
if the gas is not oxygen,
the flames will smother
- Testing for
gases can be
dangerous
- Some gases
are pretty
nasty
- Tests should be
carried out in
fume cupboards
for safety
- Carbon dioxode
- Limewater will turn
cloudy if CO2 is
bubbled through
- Hydrogen
- Makes a "squeaky
pop" with a lighted
splint
- The noise comes
from hydrogen
burning with
oxygen in the air
to form oxygen
- Chlorine
- Damp blue litmus
paper will bleach
and turn white
- The paper
may turn
red first as
chlorine is
acidic
- Tests for anions
- Sulfates
- Add barium chloride
solution then a white
barium sulate
precipitate will form
- Ba2+ +SO42 => BaSO4
- The BaSO4 will not react
with the HCl, so the white
precipitate will not dissolve
- Halide ions
- Add dilute nitric acid (HNO3) then
some silver nitrate solution and
precipitates should form
- Chloride gives a white
precipitate AgCl
- Bromide gives a cream
precipitate AgBr
- Iodide gives a yellow
precipitate AgI
- Carbonates
- Add barium chloride
solution then a white
barium carbonate
precipitate will form
- Next add HCl and if
carbonates are
present, it will fizz
producing CO2 gas
- BaCO + 2H+ => Ba2+ + CO2 + H2O
- You can test for
Carbon dioxide
with the
limewater test
- Tests for cations
- The flame test can
identify metal ions
- Lithium, Li+,
crimson red
- Sodium,
Na+, yellow
- Potassium,
K+, Lilac
- Calcium, Ca2+,
brick red
- Copper, Cu2+,
blue-green
- Some metal ions
form a coloured
precipitate with
NaOH
- you add a few drops of
sodium hydroxide solution
to your compound. If a
hydroxide precipitate forms,
you can use the colour to
figure out the ion.
- Calcium,
Ca2+, white
- Ca2+ + 2OH- => Ca(OH)2
- Copper,
Cu2+, Blue
- Cu2+ + 2OH- => Cu(OH)2
- Iron, Fe2+,
Green
- Fe2+ + 2OH- => Fe(OH)2
- Iron, Fe3+,
Brown
- Fe3+ + 3OH- => Fe(OH)3
- Zinc, Zn2+, white at
first then dissolves
in excess NaOH to a
colourless solution
- Zn2+ + 2OH- => Zn(OH)2
- Zn(OH)2 + 2OH- => Zn(OH)4 2-