Ionisation Energy Tutorial Questions & Answers PDF

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First Ionisation Energy: 1. The first ionisation energy of sodium is 494 kJ mol-1. Write the equation which represents the reaction occurring during the first ionisation energy of sodium. Answer: Na (g) → Na+ (g) + eNote: The state symbol is essential.

2. Hydrogen has an electronic structure of 1s1; helium is 1s2. Explain why helium's first ionisation energy (2370 kJ mol-1) is much higher than hydrogen's (1310 kJ mol-1). Answer: Helium's first ionisation energy is much higher than hydrogen, because the helium’s nucleus has 2 protons attracting the electrons instead of 1.

3. One of the factors which affects first ionisation energy is the nuclear charge. Lithium has 1 proton more than helium (and so a greater nuclear charge), and yet its first ionisation energy is much lower (519 kJ mol-1). Explain why. Answer: Lithium electronic configuration is 1s2 2s1. The 2s electron (the one which will be removed) is further from the nucleus, and screened by the 1s electrons. This offsets any extra attraction due to the extra proton. Helium electronic configuration is 1s2. The 1s electron is the nearest to the nucleus. Since it has only 1 shell, there is no screening effect. Hence the electron will feel full attraction force from 2 protons in the nucleus.

4. In both Periods 2 and 3, the main trend for first ionisation energy is increasing across both periods. Explain why. Answer: Across the period, the number of protons in the nucleus increases and this will increase the attraction on electrons. Hence, ionization energy increases across both periods.

5. The first ionisation energy of each element in Period 3 is less than that for the corresponding element in Period 2. For example, magnesium in Group 2 has a first ionisation energy of 736 kJ mol-1, whereas beryllium (above it in the same group) has a first ionisation energy of 900 kJ mol-1. Using magnesium and beryllium as an example, explain why first ionisation energies in Period 3 are smaller than the corresponding ones in Period 2 (down the group). Answer: − Magnesium's electronic configuration is 1s2 2s2 2p6 3s2; beryllium's is 1s2 2s2. − The magnesium's first ionisation energy is less than beryllium's because the electron being removed is in the 3-level rather than the 2-level and is further from the attraction of the nucleus. Note: Magnesium has 8 more protons and electrons in the nucleus than beryllium, but the extra nucleus charge effect is screened by the inner electrons.

6. Explain why aluminium's first ionisation energy (577 kJ mol-1) is less than magnesium's (736 kJ mol-1). Answer: − Aluminium's electronic structure is 1s2 2s2 2p6 3s2 3p1; magnesium's is 1s2 2s2 2p6 3s2. − For Aluminium, electron is being removed from 3p orbital. − For Mgnesium, elctron is being removed from 3s orbital. − The 3p orbital is slightly further from the nucleus than 3s and the electron is attracted less by the nucleus. − Hence, aluminium’s first ionization energy is less than magnesium’s. Noted: 3p electron is also screened slightly by the 3s electrons. This effect is outweighed the effect of the extra proton (nuclear charge effect).

7. Explain why sulphur's first ionisation energy (1000 kJ mol-1) is less than that of phosphorus (1060 kJ mol-1). Answer: − Sulfur electronic structure is 1s2 2s2 2p6 3s2 3p4; phosphorus's is 1s2 2s2 2p6 3s2 3p3 − 3p4 is partially filled and less stable than half filled 3p3. − Hence, sulphur first ionization energy is less than phosphorus’s.

Successive Ionisation Energy: 1. The second ionisation energy of sodium is 4560 kJ mol-1. Write the equation which represents the reaction occurring during the second ionisation energy of sodium. Answer: Na+ (g) → Na2+ (g) + eNote: The state symbol is essential.

2. The four successive ionisation energies of beryllium are: 900 1760 14800 21000 (kJ mol-1). Explain why there is a very big increment between the second and third ionisation energies? Answer: Beryllium's electronic configuration is 1s2 2s2. The first two electrons to be removed are coming from the 2s orbital which is screened from the nucleus by the 1s electrons. The third electron is being removed from the 1s orbital which is much closer to the nucleus, and has no screening.

3. The following are all lists of successive ionisation energies for different elements. In each case, decide which group of the Periodic Table the element is to be found in. * None of these elements comes from the d-block. a) 799 2420 3660 25000 32800 Answer: Group 3 b) 736 1450 7740 10500 13600 18000 21700 25600 Answer: Group 6 c) 1000 2260 3390 4540 6990 8490 27100 31700 Answer: Group 6

4. The graph shows the first ten ionisation energies for calcium.

a) Which electron is being removed at each of these ionisations. Answer: Calcium is 1s2 2s2 2p6 3s2 3p6 4s2 1 : one of the 4s electrons 2 : the other 4s electron 3 : a paired electron from one of the 3p orbitals 4 : a paired electron from one of the other 3p orbitals 5 : a paired electron from the last 3p orbital 6 : a single electron from one of the 3p orbitals 7 : a single electron from one of the other 3p orbitals 8 : a single electron from the last 3p orbital 9 : one of the 3s electrons 10 : the other 3s electron b) Point out and explain all the changes of slope in the graph. Answer: There is a big increase between the second and third electrons being removed. This is because the third electron is being removed from the 3p orbital rather than the 4-level. It is closer to the nucleus and is only screened by the shell 1 and 2 electrons. The slope of the graph is then steady while paired electrons are taken from the 3p orbitals. The slope of the graph is again steady while all the rest of the 3p electrons are removed. Between electrons 8 and 9, there is a big increase. This is because the 3s electrons are closer on average to the nucleus than 3p ones.

The 3p electrons were also screened from the nucleus by the 3s, and so were relatively easier to remove than the 3s.

c) The eleventh ionisation energy of calcium is 57050 kJ mol-1. Explain why it is so much higher than the other values on the graph. Answer: The eleventh electron is coming from the second shell. It is much closer to the nucleus, and has much less screening from the 20 protons in the nucleus. 5. Below questions are to guide you to answer possibly confusing questions. a) Which has the greater value, the first ionisation energy of magnesium or the second ionization energy of aluminium? Answer: The second IE of Al is greater than the first IE of Mg. b) Which has the greater value, the third ionisation energy of magnesium or the third ionization energy of aluminium? Answer: The third IE of magnesium is greater than the third IE of aluminium....