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Who thought atoms were like solid spheres and when was it?
- John Dalton
- At the start of the 19th century
Who came up with the plum pudding model, when did they come up with it and what was it?
- J J Thomson
- His measurements of charge and mass showed atoms must contain smaller, negatively charged particles (electrons)
Who was Ernest Rutherford and what did he do?
- He conducted the gold foil experiment with Geiger and Marsden.
- Fired positively charged particles at a thin sheet of gold
- Expected them to be deflect back but majority weren't proving there was only a small positively charged part (the nucleus)
- Concluded atom was mostly space with a positive nucleus, surrounded by a cloud of negative electrons
Who was Niels Bohr?
- Scientists realised that the cloud of negative electrons would cause the atom to collapse
- Bohr suggested electron shells
- Suggested electrons can only exist in fixed orbits or shells and each shell has fixed energy
Describe the nucleus in an atom.
- In the middle of the atom
- Contains protons and neutrons
- Has a positive charge (due to the protons)
- Almost the whole mass of the atom is concentrated in the nucleus
What is the total mass of an atom?
About 10-23 grams
Describe the electrons in an atom.
- Move around the nucleus in electron shells
- Negatively charged
- Tiny, but cover a lot of space
- The volume of their orbit determines the size of the atom
- Virtually no mass
What is the radius of an atom?
About 10-10 metres
What charge do protons have?
What charge to neutrons have?
What charge do electrons have?
What are the mass and charge of protons?
What are the mass and charge of neutrons?
What are the mass and charge of electrons?
What does the mass number tell us?
The total number of protons and neutrons in an atom
What does the atomic number tell us?
The number of protons in an atom
How does the modern periodic table arrange the elements?
In order of ascending atomic number
What are the columns in the periodic table made up of?
Elements with similar properties
What do the groups in the periodic table mean?
- The number of electrons in the outer shell
- Group 1 elements have 1 electron
- Group 7 elements have 7 electrons
How many electrons are needed to complete the outer shell?
What do the rows in the periodic table mean?
- The number of shells the atom has
- Row/period 2 elements have 2 shells
- Row/period 5 elements have 5 shells
What is the definition for an isotope?
Isotopes are different forms of the same element, which have the same number of protons but a different number of neutrons.
Who tried to organise the elements into triads?
When did Döbereiner begin to arrange the known elements?
How did Döbereiner arrange the periodic table?
- He groups elements based on their chemical properties
- He put them in groups of three (triads)
- The middle element had the average atomic mass of the other two
What did Newlands do?
- Law of the octaves
- He noticed every eighth element had similar properties
- Grouped them in rows of 7
Why did Newlands' theory fail?
- Because he didnt leave room for unknown elements
- Transition metals messed it up
- He mixed up metals and non-metals
Who was Mendeleev and what did he do?
- Dimitri Medeleev arranged the 50 elements he had into a table
- He left gaps for unknown/missing ones
- He put them in order of atomic mass
- His gaps predicted the properties of unknown elements (when they were found they fit nicely into the table)
What evidence was there that later made Mendeleev's table make even more sense?
- Each element has an atomic number exactly one more than the previous element
- The pattern in the periodic table matches the way electrons are arranged in the atom
How many electrons are allowed in the 1st shell?
How many electrons are allowed in the 2nd shell?
How many electrons are allowed in the 3rd shell?
What do ionic bonds between metals and non-metals produce?
- Giant ionic structures
- The ions form a closely packed regular lattice arrangement
- They aren't free to move so the compounds don't conduct electricity when solid
- They are very strong chemical bonds between all the ions
How are covalent bonds formed?
Sharing pairs of electrons
What are the melting and boiling points for simple molecular substances?
- Very low because the molecules are easily parted from each other
- The atoms within the molecules are held together by very strong covalent bonds
- The forces of attraction are very weak
- Most molecular substances are gases or liquids at room temperature
- They don't conduct electricity because there are no free electrons or ions
What are group 1 metals known as?
- Alkali metals
- As you go down they become more reactive
- The outer shell is more easily lost because it's further from the nucleus so less energy is needed to remove it
- They all have 1 outer electron
What are the properties of the group 1 metals?
- Very reactive
- Low melting point
- Low boiling point
- Low density (lithium, sodium and potassium float on water)
- Very soft
- They always form ionic compounds
What is oxidation?
The loss of electrons
What happens when Lithium, Sodium or Potassium react with water?
- They react vigorously
- The move around the surface, fizzing and producing hydrogen
- Sodium and potassium melt in the heat of reaction
- An alkali forms which is the hydroxide of the metal
What are the characteristic colours of alkali metals burning?
- Lithium - Red
- Sodium - Yellow/orange
- Potassium - Lilac
Describe the process of burning alkali metal compounds.
- Dip a wire loop into some hydrochloric acid to clean and moisten it
- Put the loop into a powdered sample of the compound to be tested, then place the end into a blue Bunsen burner flame
- Alkali metals give specific coloured flames which tell you which alkali is present
What are group 7 elements known as?
What are the group 7 elements?
What happens if you go down group 7?
The halogens become less reactive
What is chlorine like at room temperature?
- Fairly reactive
- Low boiling point
What is bromine like at room temperature?
What is iodine like at room temperature?
- Dark grey
- High boiling point
What is reduction?
The gain of electrons
If halogens react with alkali metals, what is produced?
- A salt
- Also called metal halides
Discuss displacement in the group 7 halogens.
- The more reactive will displace the less reactive
- Chlorine will displace bromine and iodine
- Bromine will displace iodine
What are the basic properties of metals?
- Crystal structure
- Most have high melting and boiling points and high density
- Good conductors of heat and electricity
What are metallic bonds?
- Bonds which hold together metals
- Allow the outer electrons of each atom to move freely
- Creates a sea of delocalised electrons throughout the metal
What is malleable?
When something can be hammered into shape
Match the metals to the uses.
Saucepans - good conductor of heat, doesn't rust easily - stainless steel, cheap
Electrical wiring - good conductor of electricity, easily bent - copper
Aeroplanes - low density, strong, doesn't corrode - aluminium
Bridges - strong - steel (mostly iron, little bit or carbon makes it less brittle)
What is a superconductor?
- A metal which becomes so cold the resistance disappears completely
- None of the energy is turned into heat so none of it is wasted
- This means you could start a current flowing, remove the battery and the current would carry on flowing forever
What can you make using superconducting wires?
- Power cables that transmit electricity without any loss of power
- Really strong electromagnets that don't need a constant power source
- Electronic circuits that work really fast because there is no resistance to slow them down
What temperature do metals start superconducting?
- -265ocGetting things this cold is very hard and very expensive
Are scientists trying to make better superconductors?
- They are trying to make them work at room temperature
- So far scientists have made 'some weird metal oxide things' work at -135oc
- Ideally they want to make them work at 20oc
What are some transition metals?
How do transition metals make good catalysts?
- Iron - catalyst used in the haber process for making ammonia
- Nickel - useful for hydrogenation of alkenes (to make margarine)
What are the colours of the transition elements?
- Iron (II) compounds - light green
- Iron (III) compounds - orange/brown
- Copper compounds - blue
- Colourful due to the transition metal ion they contain
What is thermal decomposition?
When a substance breaks down into at least two other substances when heated
Give examples of transition metal carbonates.
- Copper (II) carbonate - CuCO3
- Iron (II) carbonate - FeCO3
- Zinc carbonate - ZnCO3
- Manganese carbonate- MnCO3They break down into a metal oxide and carbon dioxide (you can check if its CO2 by using limewater)
What is a precipitation reaction?
- A reaction where two solutions react and an insoluble solid forms in the reaction
- Solid is said to precipitate out and the solid is also called a precipitate
Give some examples of precipitation reactions?
copper (II) sulfate + sodium hydroxide -- copper (II) hydroxide + sodium sulfate
iron (II) sulfate + sodium hydroxide -- iron (II) hydroxide + sodium sulfate
iron (III) sulfate + sodium hydroxide -- iron (III) hydroxide + sodium sulfate
How can you use precipitation to test for transition metal ions?
- Some insoluble transition metal hydroxides have distinctive colours...
- Copper (II) hydroxide is a blue solid
- Iron (II) hydroxide is a grey/green solid
- Iron (III) hydroxide is an orange/brown solid
- You can use this information to find out what precipitate has formed
Give some examples of uses of water.
- Domestic uses - washing and drinking
- Industrial uses - as a cheap raw material, a coolant (especially in power stations) and a solvent
How much of the UKs water goes into industry?
Between half and two thirds
Where do we get our water from in the UK?
- SURFACE WATER - lakes, rivers and reservoirs. These can start to run dry in the summer months
- GROUNDWATER - aquifers (rocks that trap water underground). In parts of the South East, where surface water is limited, up to 70% of domestic water supply comes from groundwater
Describe the water purification process.
- FILTRATION - a wire mesh screens out large twigs and then gravel and sand beds filter out any other solid bits
- SEDIMENTATION - iron sulfate or aluminium sulfate is added to the water which makes fine particles clump together and settle at the bottom
- CHLORINATION - chlorine gas is bubbled through to kill harmful bacteria and other microbes
Describe some impurities of tap water.
- Some soluble impurities are not removed because they can't be filtered out. These include minerals which cause water hardness and some harmful or poisonous chemicals such as pesticides and fertilisers
- Nitrate residues from excess fertiliser 'run-off' into rivers and lakes, if too many of these get into the water it can cause serious health problems, especially for young babies. Nitrates prevent the blood from carrying oxygen properly
- Lead compounds from old lead pipes, very poisonous particularly in children
- Pesticide residues from spraying too near to rivers and lakes
How can you make sea water into fresh water?
- Distillation needs loads of energy, so it's really expensive and not practical for producing large quantities of fresh water
How do you test for sulfate ions using barium chloride?
- Add some dilute hydrochloric acid to the test sample
- Add 10 drops of barium chloride solution
- If you see a white precipitate, there are sulfate ions in the sample
How do you test for halide ions using silver nitrate?
- Add some dilute nitric acid to the test sample
- Add 10 drops of silver nitrate solution
- If halide ions are present a precipitate will form...
- Chloride ions - white
- Bromide ions - cream
- Iodine ions - pale yellow
Give water purity reactions.
silver nitrate + sodium chloride -- silver chloride + sodium nitrate
silver nitrate + sodium bromide -- silver bromide + sodium nitrate
silver nitrate + sodium iodide -- silver iodide + sodium nitrate