OCR A Jun 2009 Paper 1 Q4 (with explained solutions) |

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OCR A Jun 2009 Paper 1 Q4

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Ionisation energies have been used to develop the model of the atom. The first ionisation energies of the elements Li to Na are shown in the figure below. 1st ionisation energy / kJ mol1 2500 2000 1500 1000 500 2081 1681 1402 1314 1086 900 801 520 496 Li Be Ne Na (a) Define the term first ionisation energy.[3] (b) (i) Explain why the first ionisation energies show a general increase from Li to Ne.[3]OCR 2009<br />
(ii) Explain the difference between the first ionisation energies of Li and Na. In your answer, you should use appropriate technical terms, spelt correctly.[3] (c) The first ionisation energy of oxygen is 1314 kJ mol1 and the second ionisation energy of oxygen is 3388 kJ mol1. (i) Write an equation to represent the second ionisation energy of oxygen. Include state symbols.[1] (ii) Suggest why the second ionisation energy of oxygen has a greater value than the first ionisation energy of oxygen.[1] [Total: 11]OCR 2009 Turn over<br />

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F321 Question 4 (i) (a) (b) (i) (ii) Mark Scheme June 2009 Expected Answers the energy required to remove one electron (cid:57) from each atom in one mole (cid:57) of gaseous atoms (cid:57) Marks outer electrons closer to nucleus OR radii decreases (cid:57) nuclear charge increases OR protons increase (cid:57) electrons added to the same shell OR screening OR shielding remains the same (cid:57) atomic radii increase OR there are more shells (cid:57) there is more shielding OR more screening (cid:57) Additional Guidance ALLOW 3 marks for: the energy required to remove one mole of electrons (cid:57) from one mole of atoms (cid:57) atoms in the gaseous state (cid:57) If no definition, ALLOW one mark for the equation below, including state symbols. X(g) (cid:198) X+(g) + e / X(g)e (cid:198) X+(g) ALLOW e for electron IGNORE state symbol for electron IGNORE atomic number increases IGNORE nucleus gets bigger charge increases is not sufficient ALLOW effective nuclear charge increases OR shielded nuclear charge increases ALLOW shielding is similar ALLOW electrons in higher energy level ALLOW electrons are further from the nucleus DO NOT ALLOW more orbitals OR more sub-shells DO NOT ALLOW different shell or new shell There must be a clear comparison: e.g. more shielding, increased shielding. i.e. DO NOT ALLOW just shielding. ALLOW more electron repulsion from inner shells<br />
F321 Question (c) Mark Scheme June 2009 Marks Additional Guidance Nuclear OR proton(s) OR nucleus spelt correctly ONCE ALLOW nuclear pull IGNORE any reference to effective nuclear charge 11 answer must have state symbols ALLOW e for electron ALLOW O+(g)e- (cid:198) O2+(g) DO NOT ALLOW O+(g) + e (cid:127)(cid:111) O2+(g) + 2e IGNORE state symbol for electron ALLOW the outer electrons in an O+ ion are closer to the nucleus than an O atom DO NOT ALLOW removed from next shell down Expected Answers the nuclear attraction decreases OR Increased shielding / distance outweigh the increased nuclear charge (cid:57) (i) O+(g) (cid:127)(cid:111) O2+(g) + e (cid:57) (ii) the O+ ion, is smaller than the O atom OR the electron repulsion/shielding is smaller OR the proton : electron ratio in the 2+ ion is greater than in the 1+ ion (cid:57) Total<br />

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