A guide for A level students KNOCKHARDY PUBLISHING

Name: A guide for A level students KNOCKHARDY PUBLISHING
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Description: A guide for A level students KNOCKHARDY PUBLISHING

A guide for A level students KNOCKHARDY PUBLISHING
IONISATION ENERGY A guide for A level students 2008 SPECIFICATIONS KNOCKHARDY PUBLISHING

KNOCKHARDY PUBLISHING
IONISATION ENERGY INTRODUCTION This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards. Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... Navigation is achieved by... either clicking on the grey arrows at the foot of each page or using the left and right arrow keys on the keyboard

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 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 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.

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

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

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. He Ne Ar Kr Xe

Variation in 1st 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 kJ mol-1 494 kJ mol-1 418 kJ mol-1

Variation in 1st 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 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
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

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

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

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 1s 2s ATOMIC NUMBER 4

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 1s 2s p 1s 2s ATOMIC NUMBER 5

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

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 p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s p 1s 2s 1s 2s p 1s 2s ATOMIC NUMBER 7

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 p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s p 1s 2s p 1s 2s 1s 2s p 1s 2s ATOMIC NUMBER 8

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

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 p 1s 2s p 1s 2s p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s p 1s 2s p 1s 2s 1s 2s p 1s 2s ATOMIC NUMBER 10

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

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 p 1s 2s p 1s 2s p 1st IONISATION ENERGY / kJmol-1 1s 1s 2s p 1s 2s p 1s 2s 1s 2s p 3s 1s 2s p 1s 2s 1s 2s p 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 s2 2s2 2p6 3s2 3p6 4s2 s2 2s2 2p6 3s2 3p6 4s1 s2 2s2 2p6 3s2 3p6 s2 2s2 2p6 3s2 3p5 s2 2s2 2p6 3s2 3p4 s2 2s2 2p6 3s2 3p3 s2 2s2 2p6 3s2 3p2 s2 2s2 2p6 3s2 3p1 s2 2s2 2p6 3s2 s2 2s2 2p6 3s1 s2 2s2 2p6 s2 2s2 2p5 s2 2s2 2p4 s2 2s2 2p3 s2 2s2 2p2 s2 2s2 2p1 s2 2s2 s2 2s1 s2 s1 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

I.E. kJmol-1 Electronic configuration s2 2s2 2p6 3s2 3p6 4s2 s2 2s2 2p6 3s2 3p6 4s1 s2 2s2 2p6 3s2 3p6 s2 2s2 2p6 3s2 3p5 s2 2s2 2p6 3s2 3p4 s2 2s2 2p6 3s2 3p3 s2 2s2 2p6 3s2 3p2 s2 2s2 2p6 3s2 3p1 s2 2s2 2p6 3s2 s2 2s2 2p6 3s1 s2 2s2 2p6 s2 2s2 2p5 s2 2s2 2p4 s2 2s2 2p3 s2 2s2 2p2 s2 2s2 2p1 s2 2s2 s2 2s1 s2 s1 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

I.E. kJmol-1 Electronic configuration s2 2s2 2p6 3s2 3p6 4s2 s2 2s2 2p6 3s2 3p6 4s1 s2 2s2 2p6 3s2 3p6 s2 2s2 2p6 3s2 3p5 s2 2s2 2p6 3s2 3p4 s2 2s2 2p6 3s2 3p3 s2 2s2 2p6 3s2 3p2 s2 2s2 2p6 3s2 3p1 s2 2s2 2p6 3s2 s2 2s2 2p6 3s1 s2 2s2 2p6 s2 2s2 2p5 s2 2s2 2p4 s2 2s2 2p3 s2 2s2 2p2 s2 2s2 2p1 s2 2s2 s2 2s1 s2 s1 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

I.E. kJmol-1 Electronic configuration s2 2s2 2p6 3s2 3p6 4s2 s2 2s2 2p6 3s2 3p6 4s1 s2 2s2 2p6 3s2 3p6 s2 2s2 2p6 3s2 3p5 s2 2s2 2p6 3s2 3p4 s2 2s2 2p6 3s2 3p3 s2 2s2 2p6 3s2 3p2 s2 2s2 2p6 3s2 3p1 s2 2s2 2p6 3s2 s2 2s2 2p6 3s1 s2 2s2 2p6 s2 2s2 2p5 s2 2s2 2p4 s2 2s2 2p3 s2 2s2 2p2 s2 2s2 2p1 s2 2s2 s2 2s1 s2 s1 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.

CLICK HERE FOR THE ANSWER
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

CLICK HERE FOR THE ANSWER
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

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. Q.2

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.

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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A guide for A level students KNOCKHARDY PUBLISHING

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