in 1897 jj thomson “plum pudding” model for the atom. small negative charges (“electrons”)...
Post on 06-Jan-2018
219 Views
Preview:
DESCRIPTION
TRANSCRIPT
In 1897 JJ Thomson “Plum Pudding” model for the atom.
small negative charges (“electrons”) arranged in a sphere of positive charge.
Rutherford “gold foil experiment”.
few positively charged particles were deflected backwards.
Bohr - Each shell represents an energy level. All electron in the same shell have fixed energy
-1 charge, 0.0005 mass
+1 charge, 1 mass
0 charge, 1 mass
Relative Atomic Mass – protons and neutrons
Atomic Number –protons (also number of electrons)
Neutrons = atomic mass – atomic numberAlways the
biggest number!
Isotopes – a form of an atom with the same atomic number (same number of protons) but a different number of neutrons so it has a different relative atomic mass.
Going down the periodic table the atoms are organised into groups.
Elements in the same group have the same number of electrons in
the outer shell.
They all have similar properties because they have the same
number of electrons in the outer shell.
Going across the periodic table the atoms are arranged into periods.
Elements in the same period have the same number of shells
In 1828, Dobereiner grouped the known elements into triads based on their chemical properties.
Middle element has the atomic mass which is the mean of the total atomic mass of the triad
Newlands every 8th element had similar properties so he organised them into groups of 7 called “octaves”.
His work was not accepted because:
1) Not all elements had similar properties.
2) mixed up metals / non metals
3) no space for undiscovered elements.
Mendeleev - elements in order of atomic mass.
groups according to similar properties.
left gaps - predicted properties of undiscovered elements.
Rules for drawing electron configuration
• Atomic number tells the number of electrons around the nucleus.
• Electrons always occupy shells (also known as energy levels)
• Lowest energy levels are always filled first.
• First shell – max 2 electrons
• Second shell onwards – max 8 electrons
• Ca – 2.8.8.2
Ionic Bonding• ions strongly attracted to each other. (+ to -)
• Group 1/2 are keen to lose electrons. • Groups 6/7 are keen to gain electrons• Metal – non metal
Na loses e- = positively charged.
Cl gains e- = negatively charged.
Ionic Compounds
• giant ionic lattices• ions strongly attracted to
each other / unable to move.
• high melting / boiling points
• don’t conduct electricity when solid
• When melted or dissolved - conduct electricity – ions free to move.
• Draw the ionic bonding for:– MgO– CaCl2
Covalent Bonding (strong)• non-metal atoms - share pairs
of electrons.• The forces between molecules,
are weak• very low melting / boiling
points.• don’t conduct electricity.
Methane (CH4)
Chlorine Gas (Cl2)
Water (H2O)Hydrogen Gas (H2)
Carbon Dioxide (CO2)
Group 1 – The Alkali Metals– Group 1 Metals - 1e-
in outer shell– go down group 1 -
metals more reactive.– outer electron further
away from nucleus so less energy is needed to remove it.
– all have low melting points, low density and are very soft.
• Reacting with water:– Move around the
surface, fizzing violently, produce hydrogen.
2Na + 2H2O 2NaOH + H2
Sodium + Water Sodium Hydroxide + Water
Alkali metals burn with characteristic colours:Lithium: RedSodium: YellowPotassium: Lilac
Group 7 – The Halogens• 7 e- in outer shell.• go down group 7 - less reactive• because there is less inclination to fill the outer shell
as its further from the nucleus.• Melting / boiling points increase.• At room temp:
– Cl2 is a poisonous green gas– Br2 is a poisonous orange liquid.– I2 is a grey solid
Halogens react with Alkali metals to form Metal Salts2Na + Cl2 2NaCl
Sodium + Chlorine Sodium Chloride
Displacement ReactionsA more reactive halogen can displace a less reactive halogen from its salt
chlorine + sodium bromide → sodium chloride + bromineCl2 + 2NaBr → 2NaCl + Br2
Superconductors• At low temperatures• have little or no electrical
resistance.• benefits:
– Power transmission without loss
– Super-fast electronic circuits
– Powerful electromagnets– Superconducting
electromagnets used in hospital MRI scanners
Drawbacks:At the moment, superconductors have to be REALLY COLD. This is expensive
to achieve and takes a lot of energy.
Thermal Decomposition
• substance breaks down into two or more substances,when heated.
• Transition metal carbonates
• CuCO3 CuO + CO2• Test for carbon dioxide-
limewater-cloudy.CuSO4 + 2NaOH Cu(OH)2 + Na2SO4
Copper (II) Sulphate + Sodium Hydroxide Copper (II) Hydroxide + Sodium Sulphate
FeSO4 + 2NaOH Fe(OH)2 + Na2SO4Iron (II) Sulphate + Sodium Hydroxide Iron (II) Hydroxide + Sodium
Sulphate
Fe2(SO4)3 + 2NaOH 2Fe(OH)3 + 3Na2SO4Iron (III) Sulphate + Sodium Hydroxide Iron (III) Hydroxide + Sodium
Sulphate
Identifying transition metals• Add sodium hydroxide =
displacement reaction. • Na more reactive metal, displaces
transition metal • Transition metal hydroxide is
insoluble in water = precipitate.
Copper hydroxide: blue precipitateIron (II) Hydroxide: Grey/green precipitateIron (III) Hydroxide: Orange/Brown precipitate
WaterWater• reservoirs, lakes, rivers, bore holes, aquifers.• Pollutants get into water... Factory output, Leaks in pipes• Natural disasters• Bad sanitation• Waterborne disease• Lead pipes dissolving into the water• Pesticides• Nitrates from fertilisers
STEPS1. Sedimentation – particles drop to
the bottom2. Filtration – of particles using sand3. Chlorination – to kill microbes
PRECIPITATION reactions are used to test for the presence of IONS in water.
IONS to test for: Chemical usedSulphate SO4
2- ......... barium chloride – white precipitate
Barium chloride(aq) + sodium sulfate(aq)→sodium chloride(aq) + barium sulfate(s)
BaCl2(aq) + Na2SO4(aq) → 2NaCl(aq) + BaSO4(s)
Chloride Cl- WhiteBromide Br- ……… silver nitrate CreamIodide I- Pale Yellow
Silver nitrate(aq)+sodium bromide(aq)→sodium nitrate(aq)+silver bromide(s)
AgNO3(aq) + NaCl(aq) → NaNO3(aq) + AgCl(s) Write BALANCED symbol equations for these :
1. Silver nitrate + Sodium chloride2. Silver nitrate + Sodium bromide3. Silver nitrate + Sodium iodide
MOLESMOLES
• The mass of one mole is its molar mass (RFM in grams)
For example ... Hydrogen's RFM is 1 ... Its molar mass is 1g
• RFM is relative to 1/12 carbon
Mass (g)
Molar mass
Amount of moles
Volume (dm3)Concent
ration
Amount of moles
In 1 mole there are 6.02x10^23 particlesAvagadro’s number = 6.02x10^23
1. How many moles are there in 66g Carbon Dioxide?
2. What mass of carbon is there in 4 moles of carbon
dioxide?
Converting concentration from mol/dm3 to g/dm3 You have a solution of sulphuric
acid of 0.04mol/dm3. What is the concentration in g?STEP 1: Work out RFMH2SO4 = 98STEP 2: Convert the conc in moles to conc in grams. So in 1dm3Mass = moles x RFM0.04 x 98 = 3.92 g
• Calculate the mass of aluminium oxide when 135g of aluminium is burned in air.
• Step 1: Write the balanced equation for the reaction
• (4Al + 3O2 2Al203)
• Step 2: Calculate the moles for the part you have the information for.
(moles of aluminium = 135/ 27 = 5)
• Step 3: Look at the ratio to give you the moles for the part that you want.
(4 moles of Al react to form 2 molesAl2O3 so 5 moles would give 2.5 moles of aluminium oxide)
• Step 4: Use the equation mass = moles x Mr
(mass of aluminium oxide = 2.5 x 102 =255g)
• empirical formula shows you the simplest ratio of atoms in a compound (C2H6 would become CH3.).
• To calculate this, all you need is the experimental masses and the relative atomic mass (Ar), which is found on the periodic table.
• Example: Find the empirical formula of iron oxide when 44.8g of iron reacts with 19.2g of oxygen
• There are 5 steps:
• 1) List the elements -• 2) Write down the experimental masses -• 3) Divide each experimental mass by the Ar of each -• 4) Divide by smallest
• What is the empirical formula of • a) C7H14?
• b) C6H12O6?
• c) Al2O6?
• Find the empirical formula when:
• a) 2.4g of carbon react with 0.8g of hydrogen
• b) 21.9g of magnesium react with 29.3g of sulfur and 58.3g of oxygen
Titrations• Titrations are used to find out
exactly how much acid is needed to neutralise an alkali or vice versa.
• It can then be used to calculate unknown concentrations.
• Method:– Fill a conical flask with 25cm3
alkali of unknown concentration– Add 2-3 drops indicator– Fill a burette with acid– Using the burette add the acid a
bit at a time (say 5cm3)– When indicator changes colour
you have reached the end point. You now have a rough estimate of how much (to the nearest 5cm)
– Now repeat adding a smaller amount of acid each time.
– To increase the accuracy you need to get several consistent readings!
Titrations use single indicators so it makes it easy to see the
end point of the titration.
E.G phenolphthalein
Universal indicator is made from a mixture of different indicators so each colour indicates a range
of pH values.
• Concentration = moles x volume
• You start off with 25cm3 of sodium hydroxide that has a concentration of 0.100 moles per dm3. It takes 49cm3 of hydrochloric acid to neutralise the sodium hydroxide. What is the concentration of the hydrochloric acid used?
• Step 1: Work out how many moles of the “known” substance you have.• Number of moles = conc x volume
= 0.1 x (25/1000) = 0.0025 moles of sodium hydroxide
• Step 2: Write the balanced symbol equation for the reaction. Work out how many moles of the “unknown” stuff you had.
• NaOH + HCl NaCl + H2O• For every mole of NaOH, you need one mole of HCl• So you must need 0.0025 moles of HCl
• Step 3: Work out the concentration of the “unknown” stuff!• Concentration = no of moles / volume
= 0.0025 / (49/100) = 0.0510 mol/dm3
When you do a titration there is a gradual change in pH. At the end point there is a sudden change in pH.
The rate of a reaction can be measured by the amount of gas
produced.
Gas Syringe
Upturned measuring cylinder/burette
Mass Loss
Method Pros Cons
Gas Syringe
Can be used to collect pretty much any gas.Accurate volumes – to the nearest cm3
If the reaction is too vigorous it can blow the plunger out of the syringe.
Upturned measuring
cylinder
Cannot collect gases such as Hydrogen chloride or ammonia as these dissolve in water.
Accurate volumes – to the nearest cm3
Mass Loss Gas is released straight into the room so not suitable for reactions that produce poisonous gases.
Greater accuracy.
Time
Am
ount
of P
rodu
ct
Interpreting Rates of Reaction
Steeper gradient – faster rate of reaction
End of Reaction
More reactant
Equilibrium• Haber Process • N2 + 3H2 2NH3
• equilibrium – rate of the forward reaction is equal to the rate of the backward reaction
• closed system
Reaching an Equilibrium – the Haber Process
1)As nitrogen and hydrogen react together their concentrations fall. The initial rate of reaction
will begin to slow down.2) As more and more of the product ammonia is made, its
concentration rises and it begins to turn back into nitrogen and
hydrogen.3) As more is made, the rate of the reverse reaction speeds up. 4) After a while the forward reaction will be going at the same rate as the backward
reaction.
EquilibriumEquilibrium
• The position of the equilibrium can be in the middle, to the left or to the right.
• This tells us about the amounts of the products and reactants.• If the equilibrium is in the middle then there are the same
amounts of reactants as products.• If the equilibrium is to the right then there is more product and
not so much reactant.• If the equilibrium is to the left then there is more reactant and
not so much product.
C5
Reactant
ProductReactant
Product
Changing Equilibrium• Three factors affect the position of the equilibrium:
TemperatureFor all reversible reactions, one direction is an exothermic
reaction and the reverse direction is endothermic.• decrease temperature - rate of endothermic reaction
decreases•equilibrium will shift towards the exothermic reaction so
that more heat is produced.Pressure (only for gases)
increase pressure-equilibrium tries to reduce itequilibrium moves in the direction where there are fewer moles of gas
ConcentrationIncrease concentration-equilibrium tries to reduce this (so more product is made) = shifts to reduce this so more turns back into the reactants.
The contact processThe contact process1.)Burn sulphur in air to make
sulphur dioxide S + 02 SO22.)React sulphur dioxide with
more oxygen in air to create sulphur trioxide
2SO2 +02 2SO33. React SO3 with water to
makes sulphuric acidSO3 + H2O H2SO4
• 450 oC -compromise, forward reaction is exothermic so high temps reduce yield and shift equilibrium to left. But, at high temps rate of reaction is quicker so chemical is produced faster
• Atmospheric pressure-compromise, 3 gas molecules on the left and 2 on the right so high pressure increases yield by forcing equilibrium to the right. However, equilibrium already lies to right so the cost of thicker walls etc. to withstand higher pressure is not economical
• vanadium pentoxide (V2O5)does not affect the position of the equilibrium but makes the reaction go faster
Strong and Weak Acids• Strong Acids ionise completely in water. This means that
the compound dissociates (e.g HCl H+ + Cl-). There is a higher concentration of H+ ions ready to react.
• Weak Acids only partially ionise in water. It is a reversible reaction which sets up an equilibrium mixture.
• (e.g CH3COOH H+ + CH3OO-)• Only a few H+ ions are released at once so the
equilibrium is off to the left.• Once these H+ ions have been used up a few more are
released.• Strong acids are better electrical conductors because
they have a higher concentration of hydrogen ions to carry the charge.
Redox Reactions• Oxidation is Loss,
• Reduction is Gain• OIL RIG• Oxidising Agent – accepts
e-• Reducing Agent – donates
e-
Preventing Rusting1) Making alloys e.g steel
2) Painting and oiling/greasing
3) Galvanising – coating with a tin plate
4) Sacrificial Protection – place a more reactive metal with the iron. The water and oxygen will react with this instead.Iron + Water + Oxygen Hydrated iron(III)oxide
• Electrolysis of aqueous sulfuric acid.
• Ions: H+, OH-, SO42-
• Hydrogen ions accept electrons from the cathode to make hydrogen gas.
• At the anode, hydroxide ions lose electrons to make oxygen gas
• Products: Cathode: Hydrogen 2H+ +2e- H2Anode: Oxygen 4OH- -4e- O2 + H20
• Electrolysis of copper sulfate using carbon electrodes.
• Ions: Cu2+, H+, OH-, SO42-• Copper ions accept
electrons from the cathode to make copper.
• At the anode, hydroxide ions lose electrons to make oxygen gas
• Products: • Cathode: Copper Cu2+ +2e- CuAnode: Oxygen 4OH- -4e- O2 + H20
which anion/cation is easier to discharge?The ion discharged first is the one which is lower in the reactivity series.
What’s the link between current and charge when talking about electrolysis?• The amount of product is proportional to time and
current• Q = It• t Time (seconds)• I Current (amps)• Q Charge (coulomb)• Example question:
– A current of 0.1A for 2 hours increased the mass of an anode by 0.24g. How much charge was transferred?
http://www.youtube.com/watch?v=6UwSazq8GTU
Pollution•Contain poisonous catalyst•Burn fossil fuels to produce hydrogen and oxygen
Making EthanolFermentation•Renewable – raw material from plant material•Yeast is used to ferment glucose solution•glucose→Ethanol+Carbon Dioxide•C6H12O6 → 2C2H5OH + 2CO2•(enzyme inactive) 25 - 50 degrees (denatured)•Absence of air from fermentation prevents the formation of ethanoic acid by oxidation of the ethanol.•slow•Ethanol purified by distillation, lots of energy, expensive
Hydration•Ethene Ethanol
•Ethene passed over heated phosphoric acid catalyst with steam.•Ethene + water → Ethanol•C2H4 + H2O → C2H5OH
•non-renewable as the ethene will be made by cracking components of crude oil. •quicker
Depletion of Ozone• In stratosphere• Ozone filters out and stops harmful ultraviolet light from reaching the surface of the earth• CFCs were used as refrigerants and in aerosols because they have a low boiling point, are
insoluble in water and are very unreactive.• Use of CFCs in the UK is now banned to stop any more damage to the ozone layer.• Instead hydrocarbons (alkanes) or hydrofluorocarbons (HFCs) are now used as safer
alternatives to CFCs.• The depletion of ozone in the atmosphere allows increased levels of harmful ultraviolet light to
reach the earth and this can cause……– An increased risk of sunburn– Increased ageing of the skin– Skin cancers– Increased risk of cataracts
Free Radicals• CFC molecule is hit by UV light a chlorine atom is produced. A chlorine atom is called a free
radical.– The chlorine free radical reacts with an ozone molecule to form a chlorine oxide molecule and an
oxygen molecule
• Cl + O3 → ClO + O2 – The chlorine oxide molecule then reacts with an oxygen atom to produce a chlorine free radical and an
oxygen molecule
• ClO + O → Cl + O2 – The chlorine free radical is regenerated by this chain reaction and can go on to destroy many more
ozone molecules in a a chain reaction. Therefore a few chlorine atoms can destroy large amounts of ozone.
Water Hardness– Hard = does not lather with soap– Soft = lathers well with soap
• Calcium and magnesium ions form dissolved salts which cause hardness in water
• There are two types of hardness in water– Permanent = caused by dissolved calcium sulphate. Cannot be
removed by boiling– Temporary Calcium carbonate + water + carbon dioxide calcium hydrogencarbonateCan be removed by boilingDecomposition of Ca(HCO3)2
Ca(HCO3)2 CaCO3 + H2O + CO2 (insoluble limescale)Removes temp. and permanent1. Ion Exchange resin –- sodium ions come off the resin and go into the
water, while calcium ions come out of the water and stick to the resin 2. Washing Soda – Na2CO3
Ca2+(aq) + CO3
2–(aq)→ CaCO3(s) Insoluble Limescale
(solids) Fats and Oils (liquids)Oils and fats are ESTERS that can be obtained from animals or vegetables.
– Saturated = carbon-carbon single bonds– Unsaturated = at least one carbon-carbon double bond
Test for Unsaturated fats• Shake with bromine water : Orange to colourless Natural Fats and Oils• Animal oils/fats often saturated - Vegetable oils/fats often unsaturated• More unsaturated = reduce build up of cholesterol.Mixing Fats and Oils• Oil and water are immiscible - do not mix.• vegetable oil added to water + shaken well = emulsion.• An emulsion is one liquid finely dispersed in another • The shaking breaks up the oil into small droplets that disperse (spread out) in the
water.– Milk is an oil-in-water emulsion that is mostly water with tiny droplets of oil
dispersed in it.– Butter is a water-in-oil emulsion that is mostly oil with droplets of water dispersed
in it.Saponification - vegetable oil + hot sodium hydroxide glycerol + soap• hydrolysis - breaking up ester groups in the oil molecule using an alkali• Margarine : vegetable oil + hydrogen : nickel catalyst solid saturated fat
Detergents• hydrophilic head forms strong intermolecular forces with water molecules• hydrophobic tail forms strong intermolecular forces with fat and oil molecules
Dry cleaning • A greasy stain may be removed using dry cleaning solvent.• There are weak intermolecular forces between the grease molecules, and
there are weak intermolecular forces between the solvent molecules.• The solvent molecules can also form intermolecular forces with the grease
molecules. This lets the solvent molecules surround the grease molecules.
top related