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IONISATION ENERGY

IONISATION ENERGY. -. Attraction between the nucleus and an electron. WHAT IS IONISATION ENERGY?. Ionisation Energy is a measure of the amount of energy needed to remove electrons from atoms.

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IONISATION ENERGY

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  1. IONISATION ENERGY

  2. - Attraction between the nucleus and an electron WHAT IS IONISATION ENERGY? Ionisation Energy is a measure of the amount of energy needed to remove electrons from atoms. As electrons are negatively charged and protons in the nucleus are positively charged, there will be an attraction between them. The greater the pull of the nucleus, the harder it will be to pull an electron away from an atom.

  3. - Attraction between the nucleus and an electron WHAT IS IONISATION ENERGY? Ionisation Energy is a measure of the amount of energy needed to remove electrons from atoms. As electrons are negatively charged and protons in the nucleus are positively charged, there will be an attraction between them. The greater the pull of the nucleus, the harder it will be to pull an electron away from an atom. FIRST IONISATION ENERGY - Definition The energy required to remove ONE MOLE of electrons from ONE MOLE of gaseous atoms to form ONE MOLE of gaseous positive ions. e.g. Na(g) Na+(g) + e- Al(g) Al+(g) + e- Make sure you write in the (g)

  4. WHAT AFFECTS IONISATION ENERGY? The value of the 1st Ionisation Energy depends on the electronic structure Hydrogen Helium Lithium 1310 kJ mol-1 2370 kJ mol-1 519 kJ mol-1 The value for helium is higher than that for hydrogen because there are now two protons in the nucleus. The nuclear charge is greater so the pull on the outer electrons is larger. More energy will be needed to pull an electron out of the atom.

  5. WHAT AFFECTS IONISATION ENERGY? The value of the 1st Ionisation Energy depends on the electronic structure Hydrogen Helium Lithium 1310 kJ mol-1 2370 kJ mol-1 519 kJ mol-1 • The value for helium is higher than that for hydrogen because there are now two protons in the nucleus. The nuclear charge is greater so the pull on the outer electrons is larger. More energy will be needed to pull an electron out of the atom. • Lithium atoms have 3 protons so you would expect the pull on electrons to be greater. However, the 1st Ionisation Energy of lithium is lower than that of helium because… • Filled inner shells exert a SHIELDING EFFECT; lowers the effective nuclear pull • FURTHER AWAY from the nucleus = lower nuclear attraction for an electron

  6. Variation in 1st Ionisation Energy - PERIODS 1st Ionisation Energy shows a ‘general increase’ across a given period

  7. He Ne Ar Kr Xe Variation in 1st Ionisation Energy - PERIODS 1st Ionisation Energy values show a periodic trend. There is a ‘general increase’ across a period before the value drops dramatically for the start of another period. The values get smaller down groups as the electron removed comes from an orbital further from the nucleus - there is more shielding.

  8. Variation in 1st Ionisation Energy - GROUPS GROUP IValuedecreases down the Group despite an increased nuclear charge the outer s electron is easier to remove this is due toincreased shieldingandgreater distancefrom the nucleus the outer electron is held less strongly and easier to remove Li Na K 519 kJ mol-1 494 kJ mol-1 418 kJ mol-1

  9. Variation in 1st Ionisation Energy - GROUPS GROUP IValuedecreases down the Group despite an increased nuclear charge the outer s electron is easier to remove this is due toincreased shieldingandgreater distancefrom the nucleus the outer electron is held less strongly and easier to remove Li Na K 519 kJ mol-1 494 kJ mol-1 418 kJ mol-1 GROUP IISimilar trend to Group I Group II values are greater than their Group I neighbours increased nuclear charge = stronger pull on electron more energy required to remove an electron

  10. Starter Define the 1st ionisation energy is: ________________________________________________________________________________________________________________________________________________________________________________________Write an example equation using magnesium: ______________________________________________

  11. Ionisation Energies continued What are the 3 things to consider/mention when considering the ionisation energy: 1) 2) 3)

  12. Variation in 1st Ionisation Energy HYDROGEN EXPLANATION Despite having a nuclear charge of only 1+, Hydrogen has a relatively high 1st Ionisation Energy as its electron is closest to the nucleus and has no shielding. 1st IONISATION ENERGY / kJmol-1 1s ATOMIC NUMBER 1

  13. 1s Variation in 1st Ionisation Energy HELIUM EXPLANATION Helium has a much higher value because of the extra proton in the nucleus. The additional charge provides a stronger attraction for the electrons making them harder to remove. 1st IONISATION ENERGY / kJmol-1 1s ATOMIC NUMBER 2

  14. 1s Variation in 1st Ionisation Energy LITHIUM EXPLANATION There is a substantial drop in the value for Lithium. This is because the extra electron has gone into an orbital in the next energy level. Despite the increased nuclear charge, the effective nuclear charge is less because of the shielding effect of filled inner 1s energy level. The 2s electron is also further away from the nucleus. It is held less strongly and needs less energy for removal. 1st IONISATION ENERGY / kJmol-1 1s 1s 2s ATOMIC NUMBER 3

  15. 1s 1s 2s Variation in 1st Ionisation Energy BERYLLIUM EXPLANATION The value for Beryllium is higher than for Lithium due to the increased nuclear charge. There is no extra shielding. 1st IONISATION ENERGY / kJmol-1 1s 1s 2s ATOMIC NUMBER 4

  16. 1s 1s 2s Variation in 1st Ionisation Energy BORON EXPLANATION There is a DROP in the value for Boron. This is because the extra electron has gone into one of the 2p orbitals. The increased shielding makes the electron easier to remove It was evidence such as this that confirmed the existence of sub-shells. If there hadn’t been any sub-shell, the value would have been higher than that of Beryllium. 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s ATOMIC NUMBER 5

  17. 1s 1s 2s Variation in 1st Ionisation Energy CARBON EXPLANATION The value increases again for Carbon due to the increased nuclear charge. The extra electron does not pair up with the previous one in the same orbital but occupies another of the 2p orbitals. This gives a lower energy configuration because there is less repulsion between the negatively charged particles. This is known as Hund’s Rule. 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s ATOMIC NUMBER 6

  18. 1s 1s 2s Variation in 1st Ionisation Energy NITROGEN EXPLANATION The value increases again for Nitrogen due to the increased nuclear charge. As before, the extra electron goes into the vacant 2p orbital. There are now three unpaired electrons. 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s ATOMIC NUMBER 7

  19. 1s 1s 2s Variation in 1st Ionisation Energy OXYGEN EXPLANATION There is a DROP in the value for Oxygen. The extra electron has paired up with one of the electrons already in one of the 2p orbitals. The repulsive force beteen the two paired-up electrons means that less energy is required to remove one of them. 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 2p 1s 2s ATOMIC NUMBER 8

  20. 1s 1s 2s Variation in 1st Ionisation Energy FLUORINE EXPLANATION The value increases again for Fluorine due to the increased nuclear charge. The 2p orbitals are almost full. 1s 2s 2p 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 2p 1s 2s ATOMIC NUMBER 9

  21. 1s 1s 2s 2p 1s 2s Variation in 1st Ionisation Energy NEON EXPLANATION The value increases again for Neon due to the increased nuclear charge. The 2p orbitals are now full so the next electron in will have to go into the higher energy 3s orbital. 1s 2s 2p 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 2p 1s 2s ATOMIC NUMBER 10

  22. 1s 1s 2s 2p 1s 2s Variation in 1st Ionisation Energy SODIUM EXPLANATION There is a substantial drop in the value for Sodium. This is because the extra electron has gone into an orbital in the next energy level. Despite the increased nuclear charge, the effective nuclear charge is less because of the shielding effect of filled inner 1s, 2s and 2p energy levels. 1s 2s 2p 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 2p 1s 2s 1s 2s 2p 3s ATOMIC NUMBER 11

  23. 1s 2s 2p 3s 1s 1s 2s 2p 1s 2s Variation in 1st Ionisation Energy MAGNESIUM EXPLANATION The value for Magnesium is higher than for Sodium due to the increased nuclear charge. There is no extra shielding. The trend is similar to that at the start of the 2nd period. 1s 2s 2p 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 2p 1s 2s 1s 2s 2p 3s ATOMIC NUMBER 12

  24. Successive Ionisation Energies Atoms with more than one electron can have them successively removed. 2nd I.E.The energy required to remove one mole of electrons (to infinity) from one mole of gaseous unipositive ions to form one mole of gaseous dipositive ions. e.g. Na+(g) Na2+(g) + e- Al+(g) Al2+(g) + e- TrendsSuccessive ionisation energies are always greater than the previous one Reason :- the electron is being pulled away from a more positive species Large increases occur when there is a change of shell Reason :- there is a big decrease in shielding Large increases can be used to predict the group of an unknown element Make sure you write in the (g) See next slide for an example

  25. Successive Ionisation Energies of Calcium I.E. kJmol-1 Electronic configuration 1 590 1s2 2s2 2p6 3s2 3p6 4s2 2 1145 1s2 2s2 2p6 3s2 3p6 4s1 3 4912 1s2 2s2 2p6 3s2 3p6 4 6474 1s2 2s2 2p6 3s2 3p5 5 8145 1s2 2s2 2p6 3s2 3p4 6 10496 1s2 2s2 2p6 3s2 3p3 7 12320 1s2 2s2 2p6 3s2 3p2 8 14207 1s2 2s2 2p6 3s2 3p1 9 18192 1s2 2s2 2p6 3s2 10 20385 1s2 2s2 2p6 3s1 11 57048 1s2 2s2 2p6 12 63333 1s2 2s2 2p5 13 70052 1s2 2s2 2p4 14 78792 1s2 2s2 2p3 15 86367 1s2 2s2 2p2 16 94000 1s2 2s2 2p1 17 104900 1s2 2s2 18 111600 1s2 2s1 19 494790 1s2 20 527759 1s1 A The 3rd I.E. is significantly higher than the 2nd I.E. because the third electron is coming out of a 3p orbital, nearer the nucleus and subjected to less shielding. More energy is needed to overcome the attraction of the nucleus. A

  26. Successive Ionisation Energies of Calcium I.E. kJmol-1 Electronic configuration 1 590 1s2 2s2 2p6 3s2 3p6 4s2 2 1145 1s2 2s2 2p6 3s2 3p6 4s1 3 4912 1s2 2s2 2p6 3s2 3p6 4 6474 1s2 2s2 2p6 3s2 3p5 5 8145 1s2 2s2 2p6 3s2 3p4 6 10496 1s2 2s2 2p6 3s2 3p3 7 12320 1s2 2s2 2p6 3s2 3p2 8 14207 1s2 2s2 2p6 3s2 3p1 9 18192 1s2 2s2 2p6 3s2 10 20385 1s2 2s2 2p6 3s1 11 57048 1s2 2s2 2p6 12 63333 1s2 2s2 2p5 13 70052 1s2 2s2 2p4 14 78792 1s2 2s2 2p3 15 86367 1s2 2s2 2p2 16 94000 1s2 2s2 2p1 17 104900 1s2 2s2 18 111600 1s2 2s1 19 494790 1s2 20 527759 1s1 B The 11th I.E. is significantly higher than the 10th I.E. because the eleventh electron is coming out of the second main energy level, not the third. It is much nearer the nucleus and is subjected to less shielding. B

  27. Successive Ionisation Energies of Calcium I.E. kJmol-1 Electronic configuration 1 590 1s2 2s2 2p6 3s2 3p6 4s2 2 1145 1s2 2s2 2p6 3s2 3p6 4s1 3 4912 1s2 2s2 2p6 3s2 3p6 4 6474 1s2 2s2 2p6 3s2 3p5 5 8145 1s2 2s2 2p6 3s2 3p4 6 10496 1s2 2s2 2p6 3s2 3p3 7 12320 1s2 2s2 2p6 3s2 3p2 8 14207 1s2 2s2 2p6 3s2 3p1 9 18192 1s2 2s2 2p6 3s2 10 20385 1s2 2s2 2p6 3s1 11 57048 1s2 2s2 2p6 12 63333 1s2 2s2 2p5 13 70052 1s2 2s2 2p4 14 78792 1s2 2s2 2p3 15 86367 1s2 2s2 2p2 16 94000 1s2 2s2 2p1 17 104900 1s2 2s2 18 111600 1s2 2s1 19 494790 1s2 20 527759 1s1 C The 19th I.E. is significantly higher than the 18th I.E. because the electron being removed is from the first main energy level. It is much nearer the nucleus and is subjected to no shielding - its value is extremely large. C

  28. Successive Ionisation Energies of Calcium I.E. kJmol-1 Electronic configuration 1 590 1s2 2s2 2p6 3s2 3p6 4s2 2 1145 1s2 2s2 2p6 3s2 3p6 4s1 3 4912 1s2 2s2 2p6 3s2 3p6 4 6474 1s2 2s2 2p6 3s2 3p5 5 8145 1s2 2s2 2p6 3s2 3p4 6 10496 1s2 2s2 2p6 3s2 3p3 7 12320 1s2 2s2 2p6 3s2 3p2 8 14207 1s2 2s2 2p6 3s2 3p1 9 18192 1s2 2s2 2p6 3s2 10 20385 1s2 2s2 2p6 3s1 11 57048 1s2 2s2 2p6 12 63333 1s2 2s2 2p5 13 70052 1s2 2s2 2p4 14 78792 1s2 2s2 2p3 15 86367 1s2 2s2 2p2 16 94000 1s2 2s2 2p1 17 104900 1s2 2s2 18 111600 1s2 2s1 19 494790 1s2 20 527759 1s1 C B A SUMMARYWherever there has been a large increase in Ionisation Energy there has been a change in energy levelfrom which the electron has been removed.

  29. QUESTION TIME Q.1 Which has the higher value, the 3rd I.E. of aluminium or the 3rd I.E. of magnesium? CLICK HERE FOR THE ANSWER

  30. QUESTION TIME Q.2 Which has the higher value, the 1st I.E. of sodium or the 2nd I.E. of magnesium? CLICK HERE FOR THE ANSWER

  31. QUESTION TIME Q.1 Which has the higher value, the 3rd I.E. of aluminium or the 3rd I.E. of magnesium? Ans The 3rd I.E. of magnesium EXPLANATION The 3rd I.E. of aluminium involves the following change... Al2+(g) Al3+(g) 1s2 2s2 2p6 3s11s2 2s2 2p6 The 3rd I.E. of magnesium involves the following change… Mg2+(g) Mg3+(g) 1s2 2s2 2p6 1s2 2s2 2p5 Despite magnesium having 12 protons in its nucleus and aluminium having 13, more energy is required to remove the third electron from magnesium. This is because the electron being removed is coming from an orbital closer to the nucleus. There is less shielding and therefore a greatereffectivenuclear charge. The electron is thus held more strongly. Q.2

  32. QUESTION TIME Q.2 Which has the higher value, the 1st I.E. of sodium or the 2nd I.E. of magnesium? Ans The 2nd I.E. of magnesium EXPLANATION The 1st I.E. of sodium involves the following change Na(g) Na+(g) 1s2 2s2 2p6 3s11s2 2s2 2p6 The 2nd I.E. of magnesium involves the same change in electron configuration… Mg+(g) Mg2+(g) 1s2 2s2 2p6 3s11s2 2s2 2p6 However, magnesium has 12 protons in its nucleus, whereas sodium only has 11. The greater nuclear charge means that the electron being removed is held more strongly and more energy must be put in to remove it.

  33. REVISION CHECK What should you be able to do? Recall the definition of 1st Ionisation Energy Understand why energy is needed to remove an electron from an atom / ion Write equations representing 1st Ionisation Energy Know the trend in 1st Ionisation Energy across periods Explain, in terms of electron configuration, the trend across a given period Know the trend in 1st Ionisation Energy down groups Explain the trend down a given group Know, and explain, why successive Ionisation Energies get bigger Explain why there is sometimes a large jump between successive values Predict which group an element is in from its Ionisation Energies CAN YOU DO ALL OF THESE? YES NO

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