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AS Chemistry 2006

AS Chemistry 2006. Revision session 2. Ionisation energies. Define the term ionisation energy (3 marks) Write an equation to show the first ionisation enthalpy of Element “E” including state symbols (3 marks)

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AS Chemistry 2006

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  1. AS Chemistry 2006 Revision session 2

  2. Ionisation energies • Define the term ionisation energy (3 marks) • Write an equation to show the first ionisation enthalpy of Element “E” including state symbols (3 marks) • The enthalpy change when 1 electron is removed from 1 mole of atoms in the gaseous state. • E(g) E+(g) + e-

  3. Complete the table for these isotopes of oxygen

  4. Ionisation energies 3 • Given your answers to the table, would you expect the first ionisation enthalpies for each of the isotopes to be similar or different? • Explain your answer

  5. Ionisation enthalpies 4 • They would be basically the same- as they each have the same number of protons (and electrons) so each has the same nuclear charge holding the electrons- so equal amounts of energy would be needed to remove 1 mole of electrons in each case. • If you are uncertain-ask!!

  6. Ionisation enthalpies 5

  7. Ionisation enthalpies 6 • Explain why the 1st IE is higher for • (i) Ne compared to Ar • (ii) Be compared to Li • (iii) Be compared to B

  8. Ionisation enthalpies still! • (i) Ar has an extra shell of electrons so there is a less strong pull from the positively charged protons, and there is also more shielding which reduces the pull still further therefore it is easier to remove the electron(s) • Therefore Ar has a lower IE (Ne is higher)

  9. (ii) Be has an extra proton in its nucleus, but the extra electron has gone into the same shell (the 2nd). So the extra electron is no further away from a stronger pull • (iii) No idea?? Answer this first then- • Write out the spd electron configurations for the 2 elements.

  10. Finally! • Be- 1s2 2s2 • B- 1s2 2s2 2p1 • The extra electron for B is in a new sub-shell- ie at higher energy- ie further away from the nucleus- thus easier to remove • Probably too hard for AS Level- but you never know- and you did have the knowledge- you just didn’t realise!!

  11. 4f 4d 4p 3d 4s 3p 3s 2p 2s Berylium, Be 1s2 2s2 1s

  12. 4f 4d 4p 3d 4s 3p 3s 2p 2s Boron, B 1s2 2s22p1 1s

  13. An easier question • Draw the bonding in magnesium sulphide- showing the outer shell electrons only

  14. Did you get it right? • Don’t forget the following traps- • Metal + non-metal = IONIC bonding- so show the IONS!! • Show the difference between the two sets of electrons;

  15. Shapes of molecules • Draw the bonding in an ammonia molecule (outer shell electrons only) • Use this to state the bond angle, shape and explanations

  16. 109° (is good enough for your syllabus) Because it has 4 pairs of electrons which want to get as far apart as possible/ minimise repulsions And has only 3 bonding pairs of electrons Shape: Pyramidal (NOT tetrahedral) Answers-

  17. Metallic bonding • Draw a labelled picture to represent the bonding in metals and explain how it “is kept together!” • Please note I have not asked about dative bonding due to time!! But I expect your notes to cover it!

  18. Metallic Bonding Delocalised electrons Positive ions

  19. Group 2 Chemistry • Write balanced chemical equations (including state symbols) for • (i) the reaction between calcium and water • (ii) the thermal decomposition of strontium carbonate (don’t even think about o!!) • State the trend in solubility of grp 2 hydroxides and carbonates, and the thermal stability of the grp 2 carbonates.

  20. Group 2 Chemistry • Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g) • SrCO3(s)  SrO(s)+ CO2(g) • Trends- • Decrease in solubility of the carbonates • Increase in solubility of hydroxides • Increase in thermal stability of carbonates

  21. More on group 2 • With reference to their respective electronic configurations explain why Magnesium and Calcium react in a similar way, but have different reactivities. (4 marks)

  22. An answer • They react in a similar way because they both have 2 electrons in their outer shells and it is this that governs the chemical properties of an element- so we can expect them to react in a similar way. • They are different because outer most electrons in Ca are further away from nucleus therefore lost more easily = more reactive (Ca = 4 shells : Mg 3 shells), less energy needed to remove these 2 electrons

  23. You could even.. • …have drawn out the electronic configurations to show how clever you were…. • Mg: 2,8,2 • Ca: 2,8,8,2

  24. Finally • By which property are elements arranged in the current periodic table? • PROTON NUMBER

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