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A-Level Chemistry
Module 3 - Periodic table and energy
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Le Chatilier's principle:
in
dynamic equilibrium
if there is a change in
conditions
,
equilibrium shifts
to
counteract
the
change
Equilibrium: increase of concentration of reactants
equilibrium shifts
right
increases
forward reaction
decreasing
reactants
and increasing
products
Equilibrium: decrease of concentration of reactants
equilibrium shifts
left
increasing the
reverse reaction
increasing
reactants
and decreasing
products
Equilibrium: decrease in concentration of products
equilibrium shifts
right
increase
forward reaction
increasing
products
and decreasing
reactants
Equilibrium: increase of concentration of products
equilibrium shifts
left
increasing
reversed reaction
decreasing
products
and increasing
reactants
Equilibrium: increase in temperature
equilibrium shifts to
reduce
the
temperature
favours
endothermic
reaction
Equilibrium: decrease in temperature
equilibrium shifts to
increase
the temperature
favours
exothermic reaction
Equilibrium: increase in pressure
equilibrium shifts to favour le
ss gas m
ole
Equilibrium: decrease in pressure
equilibrium shifts to favour mor
e gas mo
le
Equilibrium: catalysts
catalysts have
no effect
on equilibrium as both
forward
and
reverse
reactions are
increased
equally
mendeleev's periodic table:
60
known elements
arranged in
atomic mass
left gaps
for undiscovered elements
today's periodic table:
arranged in
atomic number
groups -
vertical
columns
periods -
horizontal vows
electron configuration:
same-grouped elements have the same no of
electrons
in the
outer
shell
same
grouped
elements have the same no of electrons in
sub-shells
ionisation energy:
the ability to
lose
an
electron
from an atom to form a
positive
ion
first ionisation energy:
the energy required to remove
1
electron in each atom from
1
mole of
gaseous
atoms to form 1 mole of 1+
gaseous ions
factors affecting ionisation energies:
nuclear charge - more
protons
more attraction
atomic radius
- closer
distance
more attraction
electron shielding
-
less
shells more attraction
successive ionisation energies
depends on electrons in the
outer shell
once
outer
shell in removed ionisation energy
increases
due to less
shielding
and
small atomic radius
trends in ionisation energies - N to O drop
in
oxygen
in the
p-orbital
electrons start to
pair
up so due to
repulsion
its easier to remove 1 electron
trends in ionisation energy: Be to B drop
boron has a
p-orbital
while beryllium doesn't, so boron has a
higher
energy
so it is easier to
remove
metallic bonding:
strong
electrostatic
attraction between
cation
and delocalised electrons due to
opposite
poles
is a giant
metallic lattice
structure
metallic bonding properties
conductivity - in solids and liquids delocalised
electron
carry
charge
points - high as lots of
energy
needed to overcome
electrostatic attractions
solubility - doesn't
dissolve
as a reaction will take place no
dissolving
giant covalent bonding:
simple
molecular lattice - N, O, S, P, F, Cl - weak
London
forces
giant
covalent lattice - C, B, Si -
strong
covalent
bonds
Diamond + Silicon conductivity
all
4
electrons are bonded to the
carbon
so there are no
delocalised
electrons to carry charge
Graphite conductivity
only
3
are bonded to carbon so
1
delocalised electron to carry
charge
Group 2:
metals are very
reactive
and do not occur in
elemental
from so naturally found in stable compounds
Group 2 REDOX reactions:
metal + oxygen = metal
oxide
metal + water = metal
hydroxide
+
hydrogen
metal + acid =
salt
+
hydrogen
Group 2 trends:
reactivity increases - more
shielding
and a
larger
atomic radius
solubility of hydroxides
increases
- due to more
hydroxide
ions
group 2 uses:
bases - can
neutralise
acids
agriculture -
calcium
hydroxide increases soil pH to
neutralise
acid in soil to produce
water
medicine - magnesium and calcium tablets treat
acid
indigestion
Halogens:
non-metals
which are very
reactive
and do not occur in their elemental form
Group 7 reactions:
redox -
oxidising
agents as it causes other species to lose electrons
displacement - non-metals displace each other depending on
halide
reactivity
Group 7 trends:
boiling point
increases
- more electrons, more
London
forces more energy
required
to break
reactivity
decreases
-
large
atomic radius,
more
shielding and
less
nuclear attraction
colour analysis on group 7s in water
chlorine -
pale
green
bromine -
orange
iodine -
brown
colour analysis on group 7s in cyclohexane
chlorine -
pale green
later
bromine -
orange
layer
iodine -
violet
layer
qualitative analysis: carbonate test
add
nitric acid
-
bubbles
formed
test if CO2 run through
lime water
to from
white precipitate
qualitative analysis: sulfate test
add
barium nitrate
-
white precipitate
forms
qualitative analysis: halide test
add
silver
nitrate
chlorine -
white
, bromine - cream, iodine -
yellow
to see clear results add
ammonia
in qualitative analysis: the order
carbonate
sulfate
halide
ammonium
qualitative analysis: ammonium test
add
sodium hydroxide
add damp
red
litmus paper - turns
blue
in qualitative analysis: why this order
carbonate -
sulfate
or halides don't produce
bubbles
sulfate -
carbonates
will form a
white
precipitate
halide -
carbonates
and sulfates will from
precipitates
enthalpy
- the measure of heat lost and gained in a chemical reaction
enthalpy change equation:
H(products)
-
H(reactants)
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