all you need_to_know_about_additional_science[1]
TRANSCRIPT
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All you need to know about All you need to know about Additional ScienceAdditional Science
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Chapters in this unitChapters in this unit• 1. Structures and bonding• 2. Structures and properties• 3. How much?• 4. Rates of reaction• 5. Energy and reactions• 6. Electrolysis• 7. Acids, alkalis and salts
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1.1 Atomic structure1.1 Atomic structure
Type of sub-atomic particle Relative charge MassProton +1 1Neutron 0 1Electron -1 Negligible
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1.1 Atomic structure1.1 Atomic structureColumns = groups
Group number = number of electrons in outer shell
Rows
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1.1 Atomic structure1.1 Atomic structure
Atomic number:
The number of protons in an atom
Mass number:
The number of protons and neutrons in an atom
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1.2 Electronic arrangement1.2 Electronic arrangement
Each shell = different energy level
Shell nearest nucleus =lowest energy level
Energy needed to overcome attractive forces between protons and electrons
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1.2 Electronic arrangement1.2 Electronic arrangement
Group 1 metals (aka alkali metals)
- Have 1 electron in outer most shell
- Soft metals, easily cut
- Reacts with water and oxygen
- Reactivity increases down the group
- Low melting and boiling points
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1.2 Electronic arrangement1.2 Electronic arrangement
Group 0/8 metals (aka noble gases)
- Have 2/8 electrons in outer most shell
- Very stable gases, no reaction
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1.2 Electronic arrangements1.2 Electronic arrangementsNo. Element Shell
1 2 3 41 Hydrogen 12 Helium 23 Lithium 2 14 Berylium 2 25 Boron 2 36 Carbon 2 47 Nitrogen 2 58 Oxygen 2 69 Fluorine 2 710 Neon 2 8
No. Element Shell1 2 3 4
11 Sodium 2 8 112 Magnesium 2 8 213 Aluminium 2 8 314 Silicon 2 8 415 Phosphorus 2 8 516 Sulphur 2 8 617 Chlorine 2 8 718 Argon 2 8 819 Potassium 2 8 8 120 Calcium 2 8 8 2
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1.3 Chemical bonding1.3 Chemical bonding• MixtureThe combined substances do not changeEasy to separate
• CompoundChemical reaction takes placeBonds form between atoms
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1.4 Ionic bonding 1.4 Ionic bonding (metal + non-metal)(metal + non-metal)
Very strong forces of attraction between positive and negative ions = ionic bond
Look!Group 1 element
Look!Group 7 element
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1.4 Ionic bonding1.4 Ionic bonding(metal + non-metal)(metal + non-metal)
Ionic bonds form a giant lattice structure
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1.5 Covalent bonding1.5 Covalent bonding(non-metal + non-metal)(non-metal + non-metal)
Simple molecules Giant structures
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1.6 Bonding in metals1.6 Bonding in metals
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2.1 – 2.4 Properties2.1 – 2.4 PropertiesIonic Simple
(covalent)Giant
(covalent)Metallic
Melting point
Boiling point
Electrical/heat conductor
Yes, whenmolten or insolution (aq)as allowsions to move
No, due to no overall charge
No – diamondYes – graphite due to delocalisedelectrons
Yes, due to delocalised electrons
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2.3 Graphite2.3 Graphite
Layers of graphite slip off and leave a mark on paper
The free e- from each C atom can move in between the layers, making graphite a good conductor of electricity
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2.4 Metal2.4 Metal
•Pure metals are made up of layers of one type of atoms
•These slide easily over one another and therefore metals can be bent and shaped
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2.5 Nanoscience2.5 Nanoscience• Structures are:
1-100 nm in size ora few hundred atoms
• Show different properties to same materials in bulk
• Have high surface area to volume ratio
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2.5 Nanoscience2.5 Nanoscience• Titanium oxide on
windowsTitanium oxide reacts with sunshine, which breaks down dirt
• Silver and socksSilver nanoparticles in socks can prevent the fabric from smelling
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3.1 Mass numbers3.1 Mass numbersMass number – atomic number = number of neutrons
E.g. Sodium23 – 11 = 12
Isotopes• Same number of protons• Different number of
neutrons
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3.2 Masses of atoms and 3.2 Masses of atoms and molesmoles
Relative atomic masses (Ar)Mass of atom compared to 12C
e.g. Na = 23, Cl = 35.5
Relative formula masses (Mr)Mass of a compound found by adding Ar of each element
e.g. NaCl = 23 + 35.5 = 58.5
Moles• A mole of any substance
always contains same number of particles
- Relative atomic mass in grams
- Relative formula mass in grams
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3.3 Percentages and formulae3.3 Percentages and formulaePercentage mass
% = mass of elementtotal mass of compound
Percentage composition / empirical formula
Al ClMass 9 35.5Ar 27 35.5Moles (9/27) = 0.33 (35.5/35.5) = 1Simplest ratio (divide by smallestnumber of moles)
(0.33 / 0.33) = 1 (1 / 0.33) = 3
Formula AlCl3
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3.4 Balancing equations3.4 Balancing equationsH2 + O2 H2O
Elements (Right-hand side)
Elements (Left-hand side)
H = H =
O = O =
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3.4 Reacting masses3.4 Reacting masses2NaOH + Cl2 NaOCl + NaCl + H2O
If we have a solution containing 100 g of sodium hydroxide, how much chlorine gas should we pass through the solution to make bleach? Too much, and some chlorine will be wasted, too little and not all of the sodium hydroxide will react.
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3.4 Reacting masses3.4 Reacting masses2NaOH + Cl2 NaOCl + NaCl + H2O 100 g ?
2NaOH Cl2Ar / Mr 80 71Ratio (80/80) = 1
1 x 100 = 100(71/80) = 0.88750.8875 x 100 = 88.75
Mass 100 g 88.75 g
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3.5 Percentage yield3.5 Percentage yieldVery few chemical reactions have a yield of 100% because:• Reaction is reversible• Some reactants produce unexpected products• Some products are left behind in apparatus• Reactants may not be completely pure• More than one product is produced and it may be difficult to separate the product we want
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3.5 Percentage yield3.5 Percentage yieldPercentage yield
% yield = amount of product produced (g) x 100%max. amount of product possible (g)
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3.5 Atom economy3.5 Atom economyThe amount of the starting materials that end up as useful products is called the atom economy
% atom economy = Mr of useful product x 100% Mr of all products
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3.6 Reversible reactions3.6 Reversible reactionsA + B C + D
= reversible reaction
e.g. iodine monochloride and chlorine gas:ICl + Cl2 ICl3
• increasing Cl2 increases ICl3
• decreasing Cl2 decreases ICl3
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3.7 Haber process3.7 Haber process• Fritz Haber invented
the Haber process• A way of turning
nitrogen in the air into ammonia
N2 + 3H2 2NH3
450oC
200 atm
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4.2 Collision theory4.2 Collision theoryCollision theoryChemical reactions only occur when reacting particles collide with each other with sufficient energy. The minimum amount of energy is called the activation energy
Rate of reaction increases if:• temperature increases• concentration or pressure increases• surface area increases• catalyst used
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4.2 Surface area4.2 Surface areaWhy?The inside of a large piece of solid is not in contact with the solution it is reacting with, so it cannot react
How?Chop up solid reactant intosmaller pieces or crush intoa powder
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4.3 Temperature4.3 TemperatureWhy?At lower temperatures, particles will collide:a) less oftenb) with less energy
How?Put more energy into reactionIncreasing the temperature by 10oC will double the rate of reaction
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4.4 Concentration4.4 ConcentrationWhy?Concentration is a measure of how many particles are in a solution. Units = mol/dm3
The lower the concentration, the fewer reacting particles, the fewer successful collisions
How?Add more reactant to the same volume of solution
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4.4 Pressure4.4 PressureWhy?Pressure is used to describe particles in gasesThe lower the pressure, the fewer successful collisions
How?Decrease the volume or Increase the temperature
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4.5 Catalysts4.5 CatalystsWhy?Expensive to increase temperature or pressureDo not get used up in reaction and can be reused
How?Catalysts are made from transition metals, e.g. iron, nickel, platinumProvide surface area for reacting particles to come together and lower activation energy
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5.1 Energy changes5.1 Energy changesExothermic reaction, e.g. respiration
• Energy ‘exits’ reaction – heats surroundings
• Thermometer readings rises
Endothermic reaction, e.g. photosynthesis
• Energy ‘enters’ reaction – cools surroundings • Thermometer readings fall
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5.2 Energy and reversible 5.2 Energy and reversible reactionsreactions
Hydrated Anhydrous copper sulphate copper sulphate + water
Exothermic reaction
Endothermic reaction
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5.3 Haber process (again!)5.3 Haber process (again!)
N2 + 3H2 2NH3
Exothermic reaction
temperature, products
temperature, products
Endothermic reaction
temperature, products
temperature, products
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5.3 Haber process (again!)5.3 Haber process (again!)
N2 + 3H2 2NH3
Smaller vol. of gas produced
pressure, products
pressure, products
Larger vol. ofgas produced
pressure, products
pressure, products
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5.3 Haber process (again!)5.3 Haber process (again!)
N2 + 3H2 2NH3
Pressure:- The higher the better- High pressure is dangerous!- Compromise by using 200-350 atm
Temperature:- Forward reaction is exothermic, so low temperature is preferred- But this makes reaction slow- Compromise by using 450OC
Catalyst:- Iron- Speeds up both sides of reaction
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6.1 Electrolysis6.1 ElectrolysisElectrolysis: splitting up using electricity
Ionic substance- molten (l)- dissolved (aq)
Non-metal ionMetal ion
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6.2 Changes at the electrodes6.2 Changes at the electrodes
Oxidation is loss Reduction is gainOIL RIG
Molten (PbBr) 2Br- Br2 + 2e- Pb2+ + 2e- PbSolution (KBr) 2Br- Br2 + 2e- 2H+ + 2e- H2
SolutionsWater contains the ions:
H+ and O2-
The less reactive element will be given off at electrode
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6.3 Electrolysing brine6.3 Electrolysing brine
At anode 2Cl- (aq) Cl2 (g) + 2e-
At cathode 2H+ (aq) + 2e- H2 (g)In solution Na+ and OH-
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6.4 Purifying copper6.4 Purifying copper
At anode 2H2O (l) 4H+ (aq) + O2 (g) + 2e-
At cathode Cu2+ (aq) + 2e- Cu (s)
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7.1 Acids and alkalis7.1 Acids and alkalis
Acids = H+ ions
Alkalis = OH- ions
Alkalis = soluble bases
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7.2 + 7.3 Salts7.2 + 7.3 Salts
Acid Formula Salt Example
Hydrochloric HCl Chloride Sodium chloride
Sulphuric H2SO4 Sulphate Copper sulphate
Nitric HNO3 Nitrate Potassium nitrate
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7.2 + 7.3 Salts – metals, bases 7.2 + 7.3 Salts – metals, bases and alkalisand alkalis
Metals: Metal(s) + acid(aq) salt(aq) + hydrogen(g)
Bases: Acid(aq) + base(aq) salt(aq) + water(l)
Alkalis: Acid(aq) + alkali(aq) salt(aq) + water(l)
Ionic equation (neutralisation): H+ + OH- H2O
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7.3 Salts – solutions7.3 Salts – solutionsSolutions: solution(aq) + solution(aq)
precipitate(s) + solution(aq)
Solid precipitate is filtered off and dried