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Atomic Structure LO • To review the mass of atoms and their size, using the term ‘Nano’ and what the standard form is. Atomic structure Rows = periods Row number = Columns = groups Group number = Atomic structure Atomic number: ………………… ………………… ………………… ………………… ………………… ………………… ………………… ………………… ………………… Mass number: ………………… ………………… ………………… ………………… ………………… ………………… ………………… ………………… ………………… Exam Practice • Describe in as much detail as possible the structure of a fluorine atom Mark Scheme 9 protons /Proton Number 9 mass / atomic number is neutral 1 10 neutrons 1 electron arrangement 2,7 / 9 electrons incorrect configurations neutral if no points scored, allow 1 mark for nucleus surrounded by electrons or nucleus contains neutrons and protons How small is an atom? • Atoms are very small, they have a radius of about 0.1 nm • That’s 1 x 10-10 m ! Standard Form • https://www.youtube.c om/watch?v=LR5o2ikiTM • Looking at the size of an atom……….. • Atoms are about a tenth of a billion of a meter!!!!! • How can we express this? Standard Form • When using very large or small numbers, scientists use the ‘powers of ten’ to express a number. • Distance at an atomic level is measured in nanometes(nm). • 1nm = 1 x 10-9m • Example (large number); 1 000 000m Written as………….. 1 x 106m • Example (small number); One millionth of a meter Written as…………… 1 x 10-6m Have a go • Write 15 000 000 in standard index form. = 1. 5 × 10 7 Write this 2 850 000 in standard index form. = 2.85 × 1 000 000 = 2.85 × 106 Write this 0.000467 in standard index form 4.67 × 10 -4 • Convert this back to ordinary numbers 3 x 104 = 30 000 How small is the nucleus compared with the whole atom? The radius of a nucleus is less than 1/10,000 of the atom! But the nucleus makes up almost all the mass of an ato nucleus . Therefore: which particles are responsible for the mass of the atom? • So an atom has a radius of 0.1nm (0.1 x 10-10) • The radius of the nucleus is about 1 x 10-14 So there is a lot of space Questions • The atomic radius of a boron atom is 9 x 10-11m Give it’s atomic radius in nanometers • Calculate the approximate radius of its nucleus (in nm), given that it will be about one ten thousandth the radius of the boron atom. Give your answer in standard form. • 0.09nm 1x10-11 – 1 x 10-9 = 1 x 10-2 = 9 x 10-2 Isotopes • Atoms of the same element always have the same number of PROTONS BUT they can have different numbers of NEUTRONS. • These are called ISOTOPES. • Always have the same atomic numbers BUT different mass numbers! • Chlorine's Ar of 35.5 is an average of the masses of the different isotopes of chlorine. This is calculated by working out the relative abundance of each isotope. For example, in any sample of Chlorine 25% will be 37 Cl and 75% 35 Cl. The relative atomic mass is therefore calculated using the equation: • (% of isotope 1 × mass of isotope 1) + (% of isotope 2 × mass of isotope 2) ÷ 100 So in the case of chlorine: (75 × 35) + (25 × 37) ∕ 100 = 2625 + 925 ∕ 100 = 35.3 What is the relative atomic mass of thallium which is made up from 30 per cent thallium-203 and 70 per cent thallium-205? • 204.4 Properties of Isotopes Isotopes an element can have different physical properties for example they can different densities and may or may not be radioactive They will always have the same chemical properties 3.2 Masses of atoms Relative atomic masses (Ar) Mass of atom compared to H Relative formula masses (Mr) Mass of a compound found by adding Ar of each element e.g. Na = 23, Cl = 35.5 1) H = 2) Mg = 3) Ti = 4) O = e.g. NaCl = 23 + 35.5 = 58.5 1) MgO 2) H2O 3) CH4 4) C6H12O6 3.3 Percentages and formulae Percentage mass % = mass of element ……………………………………………………… Percentage composition / empirical formula Al Cl Mass 9 35.5 Ar 27 35.5 Moles (9/27) = 0.33 (35.5/35.5) = 1 Simplest ratio (divide by smallest number of moles) (0.33 / 0.33) = 1 (1 / 0.33) = 3 Formula AlCl3 3.4 Balancing equations H2 + O2 H2O2 Elements (Right-hand side) Elements (Left-hand side) H= H= O= O= 3.4 Reacting masses 2NaOH + 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. 3.4 Reacting masses 2NaOH + Cl2 NaOCl + NaCl + H2O 100 g Ar / Mr Ratio Mass ? 2NaOH 80 (80/80) = 1 1 x 100 = 100 100 g Cl2 71 (71/80) = 0.8875 0.8875 x 100 = 88.75 88.75 g 3.5 Percentage yield Very 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 3.5 Percentage yield Percentage yield % yield = amount of product produced (g) x 100% max. amount of product possible (g) 3.5 Atom economy The amount of the starting materials that end up as useful products is called the atom economy % atom economy = Mr of useful product x 100% ……………………………………… 3.6 Reversible reactions A+B C+D …………… = reversible reaction e.g. iodine monochloride and chlorine gas: ICl + Cl2 ICl3 • increasing Cl2 increases ICl3 • decreasing Cl2 decreases ICl3 3.7 Haber process • Fritz Haber invented the Haber process • A way of turning nitrogen in the air into ammonia 4.2 Collision theory Collision theory Chemical 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 4.2 Surface area Why? The inside of a large piece of solid is not in contact with the solution it is reacting with, so it cannot react How? ……………………………………………………… ……………………………………………………… ……………………………………………………… 4.3 Temperature Why? At lower temperatures, particles will collide: a) …………………………………… b) …………………………………… How? Put more energy into reaction Increasing the temperature by 10oC will double the rate of reaction 4.4 Concentration Why? 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? …………………………………………………… …………………………………………………… 4.4 Pressure Why? Pressure is used to describe particles in gases The lower the pressure, the fewer successful collisions How? Decrease the ………………………… Increase the …………………………… 4.5 Catalysts Why? Expensive to increase temperature or pressure ……………………………………………………………………………………… ……………………………………………………………………………………… How? Catalysts are made from transition metals, e.g. iron, nickel, platinum Provide surface area for reacting particles to come together and lower activation energy 5.1 Energy changes Exothermic reaction, Endothermic reaction, e.g. ………………………………… e.g. ………………………………… • Energy ‘exits’ reaction – heats surroundings • Energy ‘enters’ reaction – cools surroundings • Thermometer readings rise • Thermometer readings fall 5.2 Energy and reversible reactions ……………………………………… Hydrated copper sulphate Anhydrous copper sulphate + water ………………………………………. 5.3 Haber process (again!) Exothermic reaction temperature products N2 + 3H2 Endothermic reaction temperature products temperature products 2NH3 temperature products 5.3 Haber process (again!) Smaller vol. of gas produced pressure products N2 + 3H2 Larger vol. of gas produced pressure products 2NH3 pressure products pressure products 5.3 Haber process (again!) Temperature: - Forward reaction is exothermic, so low temperature is preferred - But this makes reaction slow - Compromise by using …………… N2 + 3H2 Pressure: - The higher the better - High pressure is dangerous! - Compromise by using ………………………. 2NH3 Catalyst: - Iron - Speeds up both sides of reaction 6.1 Electrolysis Electrolysis: splitting up using electricity Ionic substance - molten ……… - dissolved ……… Non-metal ion Metal ion 6.2 Changes at the electrodes Solutions Water contains the ions: ……………………………………… The less reactive element will be given off at electrode Oxidation is loss Reduction is gain OIL RIG Molten (PbBr) 2Br- Br2 + 2e- Pb2+ + 2e- Pb Solution (KBr) 2Br- Br2 + 2e- 2H+ + 2e- H2 6.3 Electrolysing brine At anode At cathode In solution 6.4 Purifying copper At anode At cathode 7.1 Acids and alkalis Acids = H+ ions Alkalis = OH- ions Alkalis = soluble bases 7.2 + 7.3 Salts Acid Formula Salt Example Hydrochloric HCl Chloride Sodium chloride Sulphuric H2SO4 Sulphate Copper sulphate Nitric HNO3 Nitrate Potassium nitrate 7.2 + 7.3 Salts – metals, bases and 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): …………………………… 7.3 Salts – solutions Solutions: solution(aq) + solution(aq) precipitate(s) + solution(aq) Solid precipitate is …………………………………………………