Unit 3: Chemistry 3
C3.1 / The Periodic Table / C3.1 / The Periodic Table1. / In what order were the elements put in the early periodic table? / 3.1.1 / 1. / In order of increasing atomic weight.
(now we call it atomic mass)
2. / How were the elements put into columns or groups? / 2. / Elements with similar properties are in columns, known as groups.
3. / Why was this known as a periodic table? / 3. / Periodic means repeats regularly, similar properties occur at regular intervals.
4. / What were Newlands’ octaves? / 4. / John Newlands published a table showing that every eighth element had similar properties and could be grouped together.
5. / State the two main problems with the early periodic tables. / 5. / 1. They were incomplete, only 56 elements had been found by 1865 for Newlands to octave.
2. The elements were arranged by mass or weight which meant that some atoms did not fit the pattern and were put in the wrong groups.
6. / How did Mendeleev overcome these problems? / 6. / When he made his table, Mendeleev left spaces for elements that were yet to be discovered, famously Ga and Ge, so that the other elements fitted into the right groups.
7. / What did Mendeleev use to sort the elements into groups in his periodic table in 1869? / 7. / The elements were still in order of atomic weight. They were put into groups using their properties and the formulae of their compounds.
8. / Explain why scientists thought the periodic table of the elements was a curiosity at first? / 8. / The early tables were incomplete, some only worked for the first few elements.
9. / What discovery led to the modern versions of the periodic table? / 3.1.2 / 9. / The discovery of electrons, protons and neutrons early in the twentieth century.
10. / In what order were the elements put in the modern periodic table? / 10. / In order of increasing atomic number.
11. / What difference did this make to the modern periodic table? / 11. / The elements were placed in the proper groups.
12. / How does this change to the order of the elements link to atomic structure? / 12. / The periodic table could be used to work out the electronic structure of the elements as well as the number of protons and neutrons.
13. / How does the electronic structure change across each period in the table? / 13. / In period 1 the first shell is filled, in the second period the second shell is filled, etc. e.g. Li- 2.1, Be- 2.2, B- 2.3, C- 2.4…
14. / How does the electronic structure change down each group in the table? / 14. / Elements in the same group have the same number of electrons in their highest occupied electron shell (outer shell).
15. / What are the electronic structures of the group 2 metals Be, Mg, Ca? / 15. / Be – 2.2 Mg – 2.8.2 Ca – 2.8.8.2 All of the Group 2 metals have two electrons in their outer shells
16. / What information tells you the number of electrons in the outer shell of an element? / 16. / The group number. All the Group 1 elements have one electron in their outer shell, all the group 2 elements have 2, etc.
17. / How many electrons does iodine have in total and how many electrons are there in the outer shell? / 17. / Iodine has atomic number 53 so it has 53 electrons in total. It is in group 7 so iodine has seven electrons in its outer shell.
18. / Describe the density of the alkali metals, be specific about the first three? / 3.1.3 / 18. / The alkali metals have low density, the first three (Li, Na, K) all float on water
19a. / How do the alkali metals react with non-metals? / 19a. / They react with non-metals to form ionic compounds in which the metal ion carries a charge of +1.
19b. / Write an ionic equation for the reaction of the alkali metal atom in 19a. / 19b. / Li à Li+ + e- : Na à Na+ + e- : K à K+ + e-
Rb à Rb+ + e- : Cs à Cs+ + e-
20. / Describe the compounds of the alkali metals with non-metals. / 20. / The compounds are white ionic solids that dissolve in water to form colourless solutions
21. / Describe the reaction of the Lithium with water / 21. / Lithium floats and fizzes with water, releasing hydrogen gas. It forms lithium hydroxide which dissolves in water to give an alkaline solution that turns UI indicator purple.
22. / Describe the pattern of the reaction of the alkali metals with water / 22. / the further down group 1 an element is the more reactive the element;
Sodium floats, fizzes and melts.
Potassium floats, fizzes, melts and catches fire
22b. / Using M as the alkali metal atom, write an equation for the reaction with water in 22. / 22b. / 2M(s) + 2H2O(l) à 2MOH(aq) + H2(g)
2Na(s) + 2H2O(l) à 2NaOH(aq) + H2(g)
23. / Explain the pattern in reactivity going down the alkali metals. / 23. / As you go down the group the atoms get more shells and the single electron in the outer shell is further from the nucleus, so it is less tightly held and more easily lost. The elements need less activation energy to react i.e. they get more reactive
24. / What is the pattern in melting points and boiling points, going down the alkali metals? / 24. / The further down the group an element is the lower its melting point and boiling point.
25. / Compare the physical properties of the transition metals with the alkali metals. / 25. / Compared with the elements in Gp 1, transition elements have higher melting points (except for mercury) and higher densities. They are stronger and harder.
26. / Compare the chemical properties of the transition metals with the alkali metals. / 26. / Compared with the elements in Gp 1, transition elements are much less reactive and so do not react as vigorously with water or oxygen.
27. / Give the three characteristic properties of transition metals. / 27. / Many transition elements have ions with different charges; form coloured compounds and are useful as catalysts.
28. / What is the collective name for the group 7 elements? / 28. / They are known as the halogens.
29. / What happens when a group 7 element to form an ion? / 29. / The halogen atom becomes a halide ion. E.g. iodine atoms become iodide ions.
30. / How do the group 7 elements react with metals? / 30. / They react to form ionic compounds in which the halide ion carries a charge of –1.
31 / Write an ionic equation for the reaction of the halogen atom in Q30. / 31 / F + e- à F- : Cl + e- à Cl- : Br + e- à Br- :
I + e- à I- : At + e- à At- :
32 / Describe the trend in colour and state going down group 7 / 32 / The halogens get denser and the colours get more intense. F2 is a yellow gas, Cl2 is a green gas, Br2 is an orange liquid, I2 is a deep purple solid.
33 / Describe the trend in melting point and boiling point going down group 7 / 33 / In Group 7, the further down the group an element is the higher its melting point and boiling point.
34 / What is the rule for displacement reactions of the halogens? / 34 / A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt. Chlorine water displaces bromine from bromide solutions.
35 / Give a symbol equation to illustrate the rule? / 35 / Cl2(aq) + 2KBr(aq) à 2KCl(aq) + Br2(aq)
Cl2(aq) + 2KI(aq) à 2KCl(aq) + I2(aq)
36 / What is the trend in reactivity in group 7? / 36 / In Group 7, the further down the group an element is the less reactive the element
37 / Explain the trend in reactivity in group 7? / 37 / The trend in reactivity in gp 7 can be explained because the higher the energy level of the outer electrons the less easily electrons are gained. OR the gp 7 elements react by gaining/stealing electrons; in smaller atoms the nucleus is more effective at stealing electrons.
3.2 / Water / 3.2 / Water
1. / Is the water that we drink pure and safe? Explain your answer. / 3.2.1 / 1. / The water we drink is not pure because it contains dissolved substances. It should be safe to drink treated water as it does not contain anything that could harm us.
2. / What is soft water? / 2. / Soft water readily forms lather with soap.
3. / What is hard water? / 3. / Hard water reacts with soap to form scum and so more soap is needed to form lather.
4. / What are soapless detergents? / 4. / Soapless detergents do not form scum.
5. / What causes hard water? / 5. / Hard water contains dissolved compounds, usually of calcium or magnesium, from the rocks that the water comes into contact with.
6. / What is the difference between permanent and temporary hard water? / 6. / Permanent hard water stays hard when it is boiled. Temporary hard water is softened by boiling.
7. / What causes temporary hard water and why is it treatable? / 7. / It contains hydrogencarbonate ions (HCO3––). These decompose on heating to produce carbonate ions which react with Ca2+ and Mg2+ ions to form precipitates that remove the hardness as limescale.
8. / What are the disadvantages of hard water? / 8. / Using it can increase costs because more soap is needed. When temporary hard water is heated it produces scale that coats heating elements and reduces the efficiency of heating systems and kettles.
9. / What are the advantages of hard water? / 9. / Calcium cmpds are good for the growth and maintenance of bones and teeth; they help to reduce heart disease; it makes good tea!
10. / How does sodium carbonate soften hard water? / 10. / It reacts with the Ca2+ and Mg2+ ions to form a precipitate of calcium or magnesium carbonate
11. / How do ion exchange columns soften hard water? / 11. / Ion exchange columns contain sodium ions, which replace the calcium and magnesium ions when hard water passes through the column.
12. / Why do you need to put salt into a dishwasher regularly? / 12. / The sodium ions in the salt exchange for the calcium ions that have built up in the dishwasher’s ion exchanger.
13. / How would you compare the hardness of two water samples? / 13. / By titrating with soap solution. i.e. add soap solution from a burette and shake the water to see if forms a lasting lather.
14. / How would you compare the effects of water softening by bath salts and ion exchange? / 14. / Take a water sample and separate it into three equal parts. Pass one through an ion exchange resin, add bath salts to the second and filter. Then compare the hardness of the three samples by titrating with soap solution.
15. / When choosing water to make into drinking water, where do you start? / 3.2.2 / 15. / By choosing an appropriate source, drinking water should have sufficiently low levels of dissolved salts and microbes; start with clean water out in the country if you can.
16. / How do you get rid of suspended solids in the water during treatment? / 16. / By passing the water through filter beds to remove any solids
17. / How do you get rid of the microbes in water during water treatment? / 17. / By sterilising with chlorine.
18. / Why is fluoride added to drinking water? / 18. / Fluoride may be added to improve dental health though this is controversial.
19. / Why is chlorine added to drinking water? / 19. / To kill/sterilise the pathogens/microbes
20. / Why is drinking water neutralised during treatment? / 20. / Acids taste sour; alkalis taste soapy, neutral water has no taste.
21. / Some people use water filters on their tap water, what do they filter out? / 21. / They remove some dissolved substances from tap water to improve the taste and quality.
22. / What is in commercial water filters? / 22. / They contain activated charcoal (carbon), silver and ion exchange resins
23. / Some people make drinking water using distillation, what does this mean? / 23. / Water, even seawater, is boiled. The steam is condensed as pure water.
24. / Explain why distillation is an expensive way to make drinking water. / 24. / A large amount of energy is needed to boil the water so high costs are involved.
25. / Suggest an area of the world that might use distillation to make water. / 25. / Somewhere wealthy, The Gulf States.
3.3 / Energy changes / 3.3 / Energy changes
1. / What are the units of energy? / 3.3.1 / 1. / Joules, J, or kilojoules, kJ. Calories are used for food, one calorie is 4.2 Joules.
2. / How would you measure the energy change from burning a fuel? / 2. / The energy released when fuels burn can be measured by simple calorimetry, e.g. by heating water in a glass or metal container.
3. / What equation would you use to find a value for the energy change in Q2? / 3. / Q = mc ΔT
Energy change = mass x specific heat x temp change
4. / To what does m refer? / 4. / m is the mass of the liquid being heated
5. / How would you measure the energy change during a neutralisation reaction between an acid and an alkali? / 5. / The energy change can be calculated from the measured temperature change of the solution when the reagents are mixed in an insulated container.
6. / Draw the simple energy level diagram for an exothermic reaction / 6. /
7. / What is activation energy? (Have you shown it on the diagrams?) / 7. / The minimum amount of energy needed to start the reaction. It is shown as the distance between the energy of the reactants and the highest energy shown on the curve.
8. / Draw the simple energy level diagram for an endothermic reaction. / 8. /
9. / What is needed to break bonds in a chemical reaction? / 9. / Energy must be supplied to break bonds, i.e. bond breaking is endothermic.
10. / What is released when bonds are formed in a chemical reaction? / 10. / Energy is released when bonds are formed, i.e. bond making is exothermic.