IONISATION ENERGY CONTENTS What is Ionisation Energy? Definition of 1st 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

Before you start it would be helpful to… 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? - Attraction between the nucleus and an electron 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.

WHAT IS IONISATION ENERGY? - Attraction between the nucleus and an electron 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 (to infinity) from ONE MOLE of gaseous atoms to form ONE MOLE of gaseous unipositive ion e.g. Na(g) Na+(g) + e- Al(g) Al+(g) + e- Make sure you write in the (g)

Ionisation energy of hydrogen

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 atomic radius decreases as nuclear charge increases so attraction between nucleus and the outermost electron increases also as electrons are added to the same shell, there is not much shielding effect

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 atomic radius decreases as nuclear charge increases so attraction between nucleus and the outermost electron increases also as electrons are added to the same shell, there is not much shielding effect. 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; atomic radius increases and as there are more shells in lithium than helium so attraction between nucleus and outer most electron decreases

Helium has the most highest 1st ionization energy as : 2370 kJ mol-1 Helium has the most highest 1st ionization energy as :  Electron removed is closest / close to the nucleus Little shielding higher nuclear charge than hydrogen as more protons

Ionisation energy down the group First ionization energy decreases gradually down the group 1 as : Shielding effect increases down the group as atomic radius increases as more shells are added to the atoms down the group So less energy required to remove electron from outermost shell 519 kJ mol-1 494 kJ mol-1 418 kJ mol-1

GROUP II Similar 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

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

On moving across a period from left to right, 1. the nuclear charge of the atoms  (from +3 to +10 or +11 to +18) 2. electrons are being removed from the same shell 2,1 2,2 2,3 2,4 2,5 2,6 2,7 2,8 2,8,1 2,8,2 2,8,3 2,8,4 2,8,5 2,8,6 2,8,7 2,8,8

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

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

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

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. The value for Magnesium is higher than for Aluminum due to the increased nuclear charge. 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 1s 2s ATOMIC NUMBER 4

Variation in 1st Ionisation Energy BORON EXPLANATION There is a DROP in the value for Boron (and Aluminium) 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 1s 2s 2p 1s 2s ATOMIC NUMBER 5

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 1s 2s 2p 1s 2s ATOMIC NUMBER 6

Variation in 1st Ionisation Energy NITROGEN EXPLANATION The value increases again for Nitrogen (and Phosperous) due to the increased nuclear charge. As before, the extra electron goes into the vacant 2p orbital. There are now three unpaired electrons. Also IE is grater than of Oxygen as half full subshells are more stable 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 1s 2s 2p 1s 2s ATOMIC NUMBER 7

Variation in 1st Ionisation Energy OXYGEN EXPLANATION There is a DROP in the value for Oxygen (and Sulfur). The electrons (in the p sub-shell) are paired (for the first time). The repulsive force between 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 1s 2s 2p 1s 2s ATOMIC NUMBER 8

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 1s 2s 2p 1s 2s ATOMIC NUMBER 9

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. IE is lower than of Helium because size of Neon is bigger, this means more shielding effect by inner shells 1s 2s 2p 1s 2s 2p 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 1s 2s 2p 1s 2s ATOMIC NUMBER 10

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 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 1s 2s 2p 1s 2s 1s 2s 2p 3s ATOMIC NUMBER 11

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 1s 2s 2p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s 2p 1s 2s 2p 1s 2s 1s 2s 2p 3s 1s 2s 2p 1s 2s 1s 2s 2p 3s ATOMIC NUMBER 12

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- Trends 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 Make sure you write in the (g) See next slide for an example

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

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

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

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 SUMMARY 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 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 3s1 1s2 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 greater effective nuclear charge. The electron is thus held more strongly.

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 3s1 1s2 2s2 2p6 The 2nd I.E. of magnesium involves the same change in electron configuration… Mg+(g) Mg2+(g) 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.

ELECTRON AFFINITY Defining first electron affinity The first electron affinities of the group 7 elements          ELECTRON AFFINITY Defining first electron affinity The first electron affinity is the energy released when 1 mole of gaseous atoms each acquire an electron to form 1 mole of gaseous 1- ions. This is more easily seen in symbol terms. First electron affinities have negative values (exothermic). For example, the first electron affinity of chlorine is -349 kJ mol-1. By convention, the negative sign shows a release of energy. The first electron affinities of the group 7 elements F -328 kJ mol-1 Cl -349 kJ mol-1 Br -324 kJ mol-1 I -295 kJ mol-1

Second electron affinity The second electron affinity is the energy required to add an electron to each ion in 1 mole of gaseous 1- ions to produce 1 mole of gaseous 2- ions. This is more easily seen in symbol terms.                                                                                                  You are forcing an electron into an already negative ion. It's not going to go in willingly ! To overcome repulsion you need energy                                                                                                         The positive sign shows that you have to put in energy to perform this change. The second electron affinity of oxygen is particularly high because the electron is being forced into a small, very electron-dense space.

In electron affinity, electron is added to outer orbit of the atom In electron affinity, electron is added to outer orbit of the atom. As electron is negatively charged and brought towards positively charged nucleus , energy is released.. More shells means less electron affinity, as election affinity is exothermic if more shells are there, the electron affinity becomes more endothermic because of shielding effect and electron is added further to the nucleus

Trends in Electron Affinity Electron affinities become less negative / less exothermic / more positive (going down Group) As (added) electron is further from the nucleus OR More shielding / shielded (from the nucleus)

Electron affinity decreases or increases across a period depending on electronic configuration. This occurs because of the same subshell rule that governs ionization energies. Example: Since a half-filled "p" subshell is more stable, carbon has a greater affinity for an electron than nitrogen. Obviously, the halogens, which are one electron away from a noble gas electron configuration, have high affinities for electrons: Nitrogen has less electron affinity because electron is added to already singly occupied 2p subshell , therefore experiece a considerable repulstion and less energy is released

What should you be able to do? 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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