AQA CHEMISTRY TOPIC 1 GCSE

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+ H₂0 (1) ↑ liquid (these physical seperation techniques are used to seperate mixtures only) Soalum 个 aqueous this means that the Sodium chloride is disolved in water Sowent 0 Solution. 15 If we leave this solution For a Few days then: Nacl(aq) If we want to speed this reaction up we can gently heat our solution to evaporate the water. (However some Solids decompose when heated) _YSY_i SIMPLE DISTILLATION Simple distination is used to seperate a liquid from a solid if we want to keep the liquid. - First we evaporate the liquid by heating. - we then condense the vapour by cooling. water out OF conolense condenser 08 cold water into condenser ) weneat the solution, by using a bunsen burner, as we heal the liquid it starts to evaporate, turning into a vapour. 2) The vapour rises up the glass tube 3) The vapour then passes through the condenser. 4) This means that the vapour now. condenses, turning back into a liquid as it passes through the condenser. s) so then we collect the liquid into a beaker, So at the end we are left with crystals. of a solid in the Flask, and our liquid is. in the beaker the condenser is kept cold as we are circulating cold water around it. J C CHROMOTOGRAPHY Paper chromotography allows us to seperate substances based on their different Finding out which ceteur pen has one colour and which pens contain a mixture of Colours. 1) we take a piece of chromatography paper and draw a pencil line at the bottom. we put a dot of our first colour onto the pencil line, and next to that we put a dot of our second colour. 3) we place the bottom of the paper into a solvent. La liquid that will dissolve substances. 4) The solvent now makes up its way up the paper, and it dissolves the ink in the two colour dots, and these are now carried up the paper as well. The paper is the stationary phase because it does not move. we call the solvent the mobile phase because it does movie.. 5) After a while you may see a single spot formed up the paper, because it is only one spot, we know that it is a single pure colour. However If you see the dotted colour seperated into to two different spot, that tells us that the colour is a mixture of two different colours. A pure compound produces a single spot in all solvent. More soluble substance travels Further up the paper. why do we use draw our starting line in pencil? -If we drew the line in pen, the pen ink would move up the paper with the solvent. XXXXXXX FRACTIONAL DISTILLATION In Fractional distillation, we seperate a mixture of different liquids These liquids must have different boiling points. In the Flask we have two or more different liquids, with different boiling points. Seperating two liquids. -80% -100% 1) we start by gently heating our mixture and then both our liquids will Start to evaporate, but the one with the lower boiling point will evaporate more easily. 2) Now we have a mixture of two different vapours making their way into the Fractionating caumn. 3) when the vapour hits the fractionating column, they condense and drip back into the Flask, where the liquids evaporate again. 4) This repeated evaporation and condensation, increases the amount of the lower boiling point chemical in the Fractionating column. s) so, the lower boiling point chemical makes it way up the fractionating column, ahead of the higher boiling point chemical. 6) As the warm vapours pass up the column, they reach the thermometer, and the temp on the thermometer begins to rise. This means that a mixture of two different vapours are passing over the thermometer, although the mixture will contain more of the chemical with the lower boiling point. 7) These vapours now pass into the condenser, and they turn back into a liquid, but this is still a mixture of the two chemicals. 8) There comes a point when the temperature on the thermometer reaches the boiling point to the first chemical, and it stops rising. In this case around 80°c. At this point we have mainly one chemical passing into the condenser, so this condenses and we can collect it in a fresh beaker. This is our First proper fraction. 9) After a while the temperature on the thermometer begins to rise again, and that means that once again, a mixture of vapour is passing into the condenser, but this it mainly contains the chemical with the higher boiling point. Once the temperature becomes constant, in this case 100°c, we know that we are collecting a relatively pure sample of the second chemical. - the two chemicals are now seperated. nating er nn, ahead the different I more of d, but this ALPHA-SCATTERING EXPERIMENT The plumb pudding model suggested that an atom is a ball of positive charge with negative electrons embeded in it. the boiling 0°C 30 this roper Fraction. and that Ber, but this nperature a relatively Scientist wanted to know if the plumb pudding model was correct, to Find this out they carried out the alpha-scallering experiment. - first the scientist took a piece of gold foil. L the reason they used gold was because we can hammer gold out into very thin foil, just a few atoms thick. Scientists then Fired tiny particles at the gald, we call these alpha particles. Calpha particles have a positive charge) the first thing they noticed was that most of the alpha particles, simply passed straigh through the gold foil without changing direction foil. they noticed that most of the particles went straight through the gold etters, which told the Scientist that atoms are mainly empty space, which disproved the plumb pudding model. Secondly Secondly, because some of the alpha particles were detected, it told the scientists that the centre of the atom must have a positive charge Finally, because alpha particles sometimes bounce straight back, that told the Scientist that the centre of the atom must contain a great deal of mass. we know call the central part of an atom, the nucleus. So from these results scientists replaced the plumb pudding model with the nucleur model. mostly empty Space centre hasa tiny positive nucleus. and around the edge there's negative electrons. JYXXXXXX ATOMIC NUMBER AND MASS NUMBERE 7 - Li 3 19 23 Na 23 Na + 11 atomic number -shows no. of protons -no-of protons = Aeutrons eleCHONS 9 electrons 9 protons mass number - tens us the total no. of neutronst protons. Il electrons 11 protons Il protons 12 neutrons 10 elections Isotopes Isotopes are atoms of an element with different number of neutrons. 12 с 6 → 6 protons 6 deutrons 13 с 6 10 neutrons 19 F 9 12 neutrons 14 с Posite ions have gained lost elections. Negative ions have gained electrons. 6 6protons 7 neutrons ions - atoms which have an overall charge. They have gained or losed electrons. 9 protons 10 neutrons ID electrons 6 protons 8 neutrons 16 0²- 8 protons 8 neutrons 10 electrons 31 P 15 4 electrons 4 protons 35 CI ISelections 15 protons 17 DHE 17 protons 18 neutions 27 AI 13 34 Be 4 13 protons 14 neunions 16 elections 5 neutrons 16 neutrons. 37 CI 17 17 protons 20 neutrons. a atomic no. L a protons L2 eletrons 12 C EL 6 4 He 2 The n energy that a periodi ( RELATIVE ATOMIC MASS The relative atomic mass is the average of the mass numbers of the different isotopes. The relative atomic mass is weighted for the abundance of each isotope How common each isotope is. Relative mass atomic = number of isotope 1 mass 16 B S 4 He 2 Ĉ atomic no. L2 protons L2 eletrons 20%. abundance 12 وں یہ с 11 B S 6 ELECTRON ENERGY LEVELS 80% abundance. 10x 20 + 11 x 80 100 Ⓡ percent Xabundance Of isotope 1 prolon 个 The number of electrons in the outer energy level, tells us the group no. that we find that element in, in the periodic table. 60 electron Ⓒ 100 mass number of isotope 2 = X percent abundance OF (Sokopez 200+ 880 100 = 10.8 electrons exist in energy levels (shells) en t each energy shell can hold a maximum level no. of electrons: 2- First shell. 8 second shell 8 - third shell 18 Fourth shell. 106XXXYY ELECTRON ENERGY LEVELS Electrons exist in energy levels (Shells) Each energy level can hold a maximum number of electrons: First energy level : 2 Second energy level : 8 Third energy level: 8 O [2] Elements with full outer energy levels are in group 0 (Noble gases) 1 H/ 1 [1] 4 He 2 Ⓡ 3 Li 3 3 [2, 1] group 1 DEVELOPMENT OF THE PERIODIC TABLE Mendeleev developed the First modern periodic table Mendeleev started by arranging all the elements in order of increasing atomic weight. However, he did two things that no-one had done before. Firstly IF ne needed to, Mendeleev would switch the order of Specific elements so they fitted the paterns of other elements in the same group. Secondly, Mendeleev realised that some elements had not been discovered. So he simply left gaps between in his periodic table where he thought an element was missing, Mendeleev was so confident that his tables correct that he actually predicted the properties of the undiscovered elements based on other elements in the same groups. A several years later, these elements were discovered. Their properties matched Mendeleev's predictions. The modern table is arranged according to atomic number, whereas Mendeleevs was ordered by atomic weight as protons had not yet been discovered. The modern tade also consists of group 0. 1 Y roups. ereas .yet GROUP O (NOBLE GASES) The noble gases are very unreactive elements ५ He 2 20 23 Ne 10 Ne= 246°c Ar = - 186 c Kr = -153 c Xe = -108c Rn = 1-62° c oo 100 G eo 40 Ar Boiling points. 18 The noble gases are very unreactive elements. This is because all noble gases have a full outer energy level. He = -289°c Toto 180 The boiling points are all lower than room temperature, this is because they are all gases The boiling points increase as the relative atomic masses increase L 10XXXXXXX METALS when metais react, they lose electrons to achieve a full outer energy level, which gives them the same electronic structure as a group o noble gas.. 00 ㅋ Li 3 o 30 O Both of these elements have 1 electron in their outer shell, that's why their in group 1 when they react, they loose their one outer election, so then they have a full outer energy level. 23 Na 11 This happens for all metais, such as elements in group 3 lose 3 electrons. - when metais react, they lose electrons to achieve a full outer energy level. This gives them the same electronic structure as a group O noble gas. Metais always Form positive ions 9 Be 4 23 Na 11 40 9 when reacted → -> when reacted 110 oo ↑ Sodium ion ·2 个 Beryllium ion. 1+ GROUP 1 (THE ALKALI METALS) All group 1 metais have 1 electron in their outer energy level. All group 1 metais react rapidly with oxygen They react more rapidly as we move down group 1. ㅋ Li 3 30 7 Li 3 个 when lithium reacts with oxygen, the outer electron From the lithium atom moves to the oxygen 30 However, all though the lithium atom now has a Full outershell, the oxygen doesn't, So another lithium atom transfers another electron from the outer shell to the Oxygen, so now both Lithium otoms and oxygen atom has a full outer energy. level NOW theres; 16 16 1+ ܗ 8 30 80 2- 1+ Equation for this reaction 44 +0₂24₂0 All group 1 metais react rapidly with chlorine. All group 1 metais recict fast with water Moving down the group, the outer electron is less attracted to the nucleus and easier to lose. This is because there is a greater distance between the positive nucleus and the negative outer electron. Also, the outer electron is shielded from the nucleus by the internal energy levels xxxXxxXxXxXxxXxXxX GROUP 7 Group 7 elements have 7 electrons in their outer energy level. Atoms react in order to achieve a full outer energy level, so if we take two atoms of a group 7 element, then they simply react with eachother to form a covalent bond. 19 9 F RMM Fluorine 38 Chlorine 71 Bromine 160 logine 254 H Q covalent bond H-CI MPос врос State of room temp -220 -188 gas -101 -29 -7 Fluoride F chloride c Bromide Br locide 1² 59 11.4 184 90 when any group 7 elements reace with a metal, the group 7 As we move down group 7, the RMM increases, therefore the sizes of the molecules get bigger. Group 7 elements Form colvalent compounds when they react with aner non-meta; atoms element gains one electron and forms a - 1 ion adds an ide on gas liquid Solid 7 Li 3 35-5 13 90 CI → This is now a Fluorine molecule F-F colvalent bond when group 7 elements react with metals they gain an electron from the metal atom; chloride ion Group 7 elements form ionic compounds when they react with metal atoms. L GROUP 7 ELEMENTS CONTINUED... The elements get less reactive as we move down group 7. Elements lower down the row gain an electron less easily compared to those towards the top, this is because there is a greater distance from the outer energy level to the nucleus. Also they are more shielded by the internal electrons. Therefore, it's harder for them to attract an election in its outer energy level, therefore it's less reactive. DISPLACEMENT REACTIONS A more reactive halogen can dispiace a less reactive nalogen From an ageous solution of its salts. more reactive Sodium + fluorine Bromide Ĵ less reactive Potassium iodide Lithium chloride + chlorine + bromine A Therefore Fluorine can dispiace the bromine like this; → Sodiumt bromine + Fluoride. Potassium + iodine chloride Lithium chloride + bromine 100xxXxXxX