IONISATION 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. 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 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 1st Ionisation Energy depends on the electronic structure HydrogenHeliumLithium 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. 519 kJ mol kJ mol kJ mol -1

WHAT AFFECTS IONISATION ENERGY? The value of the 1st Ionisation Energy depends on the electronic structure HydrogenHeliumLithium 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… SHIELDING EFFECT; Filled inner shells exert a SHIELDING EFFECT; lowers the effective nuclear pull FURTHER AWAY FURTHER AWAY from the nucleus = lower nuclear attraction for an electron 519 kJ mol kJ mol kJ mol -1

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

He Ne Ar Kr Xe 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. 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. Variation in 1st Ionisation Energy - PERIODS

GROUP I 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 519 kJ mol -1 Li 494 kJ mol kJ mol -1 NaK Variation in 1st Ionisation Energy - GROUPS

GROUP I 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 GROUP II 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 519 kJ mol -1 Li 494 kJ mol kJ mol -1 NaK Variation in 1st Ionisation Energy - GROUPS

ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 Variation in 1st Ionisation Energy 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. 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. HYDROGEN 1 1s

ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 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. 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. Variation in 1st Ionisation Energy HELIUM 2

1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 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. 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. Variation in 1st Ionisation Energy LITHIUM 3

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

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 EXPLANATION DROP 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. EXPLANATION DROP 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. Variation in 1st Ionisation Energy BORON 5

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 Variation in 1st Ionisation Energy 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. 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. CARBON 6

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 Variation in 1st Ionisation Energy 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. 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. NITROGEN 7

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 Variation in 1st Ionisation Energy EXPLANATION DROP 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. EXPLANATION DROP 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. OXYGEN 8

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

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 Variation in 1st Ionisation Energy 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. 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. NEON 10

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 1s 2s 2p 3s Variation in 1st Ionisation Energy 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. 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. SODIUM 11

1s 2s 2p 1s 2s 1s ATOMIC NUMBER 1st IONISATION ENERGY / kJmol -1 1s 2s 2p 3s Variation in 1st Ionisation Energy 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. 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. MAGNESIUM 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) Na 2+ (g) + e - Al + (g) Al 2+ (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 See next slide for an example Make sure you write in the (g)

I.E. kJmol -1 Electronic configuration s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s s 2 2s 2 2p 6 3s s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s s 2 2s s s 1 A A Successive Ionisation Energies of Calcium 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 A

B B Successive Ionisation Energies of Calcium 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 B I.E. kJmol -1 Electronic configuration s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s s 2 2s 2 2p 6 3s s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s s 2 2s s s 1

C C Successive Ionisation Energies of Calcium 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 C I.E. kJmol -1 Electronic configuration s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s s 2 2s 2 2p 6 3s s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s s 2 2s s s 1

C C B B A A Successive Ionisation Energies of Calcium SUMMARYWherever there has been a large increase in Ionisation Energy there has been a change in energy level from which the electron has been removed. I.E. kJmol -1 Electronic configuration s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p 6 4s s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s 2 3p s 2 2s 2 2p 6 3s s 2 2s 2 2p 6 3s s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s 2 2p s 2 2s s 2 2s s s 1

QUESTION TIME Ans The 3rd I.E. of magnesium EXPLANATION The 3rd I.E. of aluminium involves the following change... Al 2+ (g)Al 3+ (g) 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 The 3rd I.E. of magnesium involves the following change… Mg 2+ (g) Mg 3+ (g) 1s 2 2s 2 2p 6 1s 2 2s 2 2p 5 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. Q.2 Which has the higher value, the 3rd I.E. of aluminium or the 3rd I.E. of magnesium? Q.1

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