IONISATION ENERGY CONTENTS What is Ionisation Energy Definition

  • Slides: 35
Download presentation
IONISATION ENERGY CONTENTS • What is Ionisation Energy? • Definition of 1 st Ionisation

IONISATION ENERGY CONTENTS • What is Ionisation Energy? • Definition of 1 st Ionisation Energy • What affects Ionisation Energy? • General variation across periods • Variation down groups • Variation in the first twelve elements • Successive Ionisation Energies • Questions • Check list

IONISATION ENERGY Before you start it would be helpful to… • Recall the electronic

IONISATION ENERGY Before you start it would be helpful to… • Recall the electronic configurations of the first 36 elements • Recall the properties of the three main sub-atomic particles

WHAT IS IONISATION ENERGY? Ionisation Energy is a measure of the amount of energy

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. - Attraction between the nucleus and an electron

WHAT IS IONISATION ENERGY? - Ionisation Energy is a measure of the amount of

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. Attraction between the nucleus and an electron FIRST IONISATION ENERGY - Definition The energy required to remove ONE MOLE of electrons (to infinity) 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)

WHAT AFFECTS IONISATION ENERGY? The value of the 1 st Ionisation Energy depends on

WHAT AFFECTS IONISATION ENERGY? The value of the 1 st Ionisation Energy depends on the electronic structure Hydrogen 1310 k. J mol-1 Helium Lithium 2370 k. J mol-1 519 k. J 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.

WHAT AFFECTS IONISATION ENERGY? The value of the 1 st Ionisation Energy depends on

WHAT AFFECTS IONISATION ENERGY? The value of the 1 st Ionisation Energy depends on the electronic structure Hydrogen 1310 k. J mol-1 Helium Lithium 2370 k. J mol-1 519 k. J 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 1 st 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

Variation in 1 st Ionisation Energy - PERIODS 1 st Ionisation Energy shows a

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

Variation in 1 st Ionisation Energy - PERIODS 1 st Ionisation Energy values show

Variation in 1 st Ionisation Energy - PERIODS 1 st 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. He The values get smaller down groups as the electron removed comes from an orbital further from the nucleus - there is more shielding. Ne Ar Kr Xe

Variation in 1 st Ionisation Energy - GROUPS GROUP I Value decreases down the

Variation in 1 st Ionisation Energy - GROUPS GROUP I Value decreases down the Group despite an increased nuclear charge the outer s electron is easier to remove this is due to increased shielding and greater distance from the nucleus the outer electron is held less strongly and easier to remove Li Na K 519 k. J mol-1 494 k. J mol-1 418 k. J mol-1

Variation in 1 st Ionisation Energy - GROUPS GROUP I Value decreases down the

Variation in 1 st Ionisation Energy - GROUPS GROUP I Value decreases down the Group despite an increased nuclear charge the outer s electron is easier to remove this is due to increased shielding and greater distance from the nucleus the outer electron is held less strongly and easier to remove Li Na K 519 k. J mol-1 494 k. J mol-1 GROUP II Similar trend to Group II values are greater than their Group I neighbours increased nuclear charge = stronger pull on electron more energy required to remove an electron 418 k. J mol-1

Variation in 1 st Ionisation Energy HYDROGEN EXPLANATION 1 st IONISATION ENERGY / k.

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

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1 1 s 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. 1 s ATOMIC NUMBER 2

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1 1 s 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 1 s energy level. The 2 s electron is also further away from the nucleus. It is held less strongly and needs less energy for removal. 1 s 1 s 2 s ATOMIC NUMBER 3

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

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

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1 1 s BORON EXPLANATION There is a DROP in the value for Boron. This is because the extra electron has gone into one of the 2 p orbitals. The increased shielding makes the electron easier to remove 1 s 1 s 2 s 2 p 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. 1 s 2 s ATOMIC NUMBER 5

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

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

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

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

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1 1 s OXYGEN 1 s 2 s 2 p 1 s 1 s 2 s EXPLANATION 2 p 2 p 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 2 p orbitals. The repulsive force beteen the two paired-up electrons means that less energy is required to remove one of them. 1 s 2 s 2 p 1 s 2 s ATOMIC NUMBER 8

Variation in 1 st Ionisation Energy 1 st IONISATION ENERGY / k. Jmol -1

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

Variation in 1 st Ionisation Energy 1 s NEON 1 st IONISATION ENERGY /

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

Variation in 1 st Ionisation Energy 1 s SODIUM 1 st IONISATION ENERGY /

Variation in 1 st Ionisation Energy 1 s SODIUM 1 st IONISATION ENERGY / k. Jmol -1 1 s 2 s 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 1 s, 2 s and 2 p energy levels. 2 p 2 p 2 p 1 s 1 s 2 s EXPLANATION 2 p 2 p 1 s 2 s 2 p 3 s ATOMIC NUMBER 11

Variation in 1 st Ionisation Energy 1 s MAGNESIUM 1 st IONISATION ENERGY /

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

Successive Ionisation Energies Atoms with more than one electron can have them successively removed.

Successive Ionisation Energies Atoms with more than one electron can have them successively removed. 2 nd 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. Trends Na+(g) Na 2+(g) + e- Al+(g) Al 2+(g) + e- Make sure you write in the (g) Successive 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 See next slide for an example

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3

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

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 1 s 2 2 p 6 3 s 2 3 p 6 4 s 1 1 s 2 2 p 6 3 s 2 3 p 6 1 s 2 2 p 6 3 s 2 3 p 5 1 s 2 2 p 6 3 s 2 3 p 4 1 s 2 2 p 6 3 s 2 3 p 3 1 s 2 2 p 6 3 s 2 3 p 2 1 s 2 2 p 6 3 s 2 3 p 1 1 s 2 2 p 6 3 s 2 1 s 2 2 p 6 3 s 1 1 s 2 2 p 6 1 s 2 2 p 5 1 s 2 2 p 4 1 s 2 2 p 3 1 s 2 2 p 2 1 s 2 2 p 1 1 s 2 2 s 2 1 s 2 2 s 1 1 s 2 1 s 1 B 590 1145 4912 6474 8145 10496 12320 14207 18192 20385 57048 63333 70052 78792 86367 94000 104900 111600 494790 527759 B The 11 th I. E. is significantly higher than the 10 th 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.

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 1 s 2 2 p 6 3 s 2 3 p 6 4 s 1 1 s 2 2 p 6 3 s 2 3 p 6 1 s 2 2 p 6 3 s 2 3 p 5 1 s 2 2 p 6 3 s 2 3 p 4 1 s 2 2 p 6 3 s 2 3 p 3 1 s 2 2 p 6 3 s 2 3 p 2 1 s 2 2 p 6 3 s 2 3 p 1 1 s 2 2 p 6 3 s 2 1 s 2 2 p 6 3 s 1 1 s 2 2 p 6 1 s 2 2 p 5 1 s 2 2 p 4 1 s 2 2 p 3 1 s 2 2 p 2 1 s 2 2 p 1 1 s 2 2 s 2 1 s 2 2 s 1 1 s 2 1 s 1 C 590 1145 4912 6474 8145 10496 12320 14207 18192 20385 57048 63333 70052 78792 86367 94000 104900 111600 494790 527759 C The 19 th I. E. is significantly higher than the 18 th 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.

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3

Successive Ionisation Energies of Calcium I. E. k. Jmol-1 Electronic configuration 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 1 s 2 2 p 6 3 s 2 3 p 6 4 s 2 1 s 2 2 p 6 3 s 2 3 p 6 4 s 1 1 s 2 2 p 6 3 s 2 3 p 6 1 s 2 2 p 6 3 s 2 3 p 5 1 s 2 2 p 6 3 s 2 3 p 4 1 s 2 2 p 6 3 s 2 3 p 3 1 s 2 2 p 6 3 s 2 3 p 2 1 s 2 2 p 6 3 s 2 3 p 1 1 s 2 2 p 6 3 s 2 1 s 2 2 p 6 3 s 1 1 s 2 2 p 6 1 s 2 2 p 5 1 s 2 2 p 4 1 s 2 2 p 3 1 s 2 2 p 2 1 s 2 2 p 1 1 s 2 2 s 2 1 s 2 2 s 1 1 s 2 1 s 1 590 1145 4912 6474 8145 10496 12320 14207 18192 20385 57048 63333 70052 78792 86367 94000 104900 111600 494790 527759 SUMMARY C B A Wherever there has been a large increase in Ionisation Energy there has been a change in energy level from which the electron has been removed.

QUESTION TIME Q. 1 Which has the higher value, the 3 rd I. E.

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

QUESTION TIME Q. 2 Which has the higher value, the 1 st I. E.

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

QUESTION TIME Q. 1 Which has the higher value, the 3 rd I. E.

QUESTION TIME Q. 1 Which has the higher value, the 3 rd I. E. of aluminium or the 3 rd I. E. of magnesium? Ans The 3 rd I. E. of magnesium EXPLANATION The 3 rd I. E. of aluminium involves the following change. . . Al 2+(g) 1 s 2 2 p 6 3 s 1 Al 3+(g) 1 s 2 2 p 6 The 3 rd I. E. of magnesium involves the following change… Mg 2+(g) Mg 3+(g) 1 s 2 2 p 6 1 s 2 2 p 5 Despite magnesium having 12 protons in its nucleus and aluminium having 13, more energy is required to remove 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 greater effective nuclear charge. The electron is thus held more strongly. Q. 2

QUESTION TIME Q. 2 Which has the higher value, the 1 st I. E.

QUESTION TIME Q. 2 Which has the higher value, the 1 st I. E. of sodium or the 2 nd I. E. of magnesium? Ans The 2 nd I. E. of magnesium EXPLANATION The 1 st I. E. of sodium involves the following change Na(g) 1 s 2 2 p 6 3 s 1 Na+(g) 1 s 2 2 p 6 The 2 nd I. E. of magnesium involves the same change in electron configuration… Mg+(g) 1 s 2 2 p 6 3 s 1 Mg 2+(g) 1 s 2 2 p 6 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.

REVISION CHECK What should you be able to do? Recall the definition of 1

REVISION CHECK What should you be able to do? Recall the definition of 1 st Ionisation Energy Understand why energy is needed to remove an electron from an atom / ion Write equations representing 1 st Ionisation Energy Know the trend in 1 st Ionisation Energy across periods Explain, in terms of electron configuration, the trend across a given period Know the trend in 1 st 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

You need to go over the relevant topic(s) again Click on the button to

You need to go over the relevant topic(s) again Click on the button to return to the menu

WELL DONE! Try some past paper questions

WELL DONE! Try some past paper questions

IONISATION ENERGY THE END © 2002 JONATHAN HOPTON & KNOCKHARDY PUBLISHING

IONISATION ENERGY THE END © 2002 JONATHAN HOPTON & KNOCKHARDY PUBLISHING