IONISATION ENERGY

IONISATION IONISATION ENERGYENERGY

WHAT IS 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.

-

Attraction between the nucleus and an

electron

WHAT IS 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.

-

Attraction between the nucleus and an

electron

FIRST IONISATION ENERGY - DefinitionFIRST IONISATION ENERGY - DefinitionThe 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)

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

Hydrogen Helium Lithium

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-1

1310 kJ mol-1 2370 kJ mol-1

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

Hydrogen Helium Lithium

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 EFFECTSHIELDING EFFECT;; lowers the effective nuclear pull

• FURTHER AWAYFURTHER AWAY from the nucleus = lower nuclear attraction for an electron

519 kJ mol-1

1310 kJ mol-1 2370 kJ mol-1

1st Ionisation Energy shows a ‘general increase’ across a given period

Variation in 1st Ionisation Energy - PERIODS

0

500

1000

1500

2000

2500 He

Ne

ArKr

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.

Variation in 1st Ionisation Energy - PERIODS

GROUP IGROUP 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-1418 kJ mol-1

Na K

Variation in 1st Ionisation Energy - GROUPS

GROUP IGROUP 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 IIGROUP 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-1418 kJ mol-1

Na K

Variation in 1st Ionisation Energy - GROUPS

StarterDefine the 1st ionisation energy is:

________________________________________________________________________________________________________________________________________________________________________________________

Write an example equation using magnesium:

______________________________________________

Ionisation Energies continued

What are the 3 things to consider/mention when considering the ionisation energy:

1)

2)

3)

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-1Variation 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.

HYDROGEN

1

1s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-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.

Variation in 1st Ionisation Energy

HELIUM

2

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-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.


LITHIUM

3

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-1

EXPLANATION

The value for Beryllium is higher than for Lithium due to the increased nuclear charge. There is no extra shielding.


BERYLLIUM

4

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-1

EXPLANATION

There is a DROPDROP 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.


BORON

5

1s 2s 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol


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 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol


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 2p

1s 2s 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol


EXPLANATION

There is a DROPDROP 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 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol


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 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol


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 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-1

1s 2s 2p 3s


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 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s 2p

1s 2s

1s 2s

1s

1s

ATOMIC NUMBER

1st I

ON

ISA

TIO

N E

NER

GY

/ kJ

mol

-1

1s 2s 2p 3s

1s 2s 2p 3s


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 moleof 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 oneReason :- the electron is being pulled away from a more positive species

Large increases occur when there is a change of shellReason :- 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 exampleSee next slide for an example

Make sure you write in the (g)

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

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

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


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


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 electronhas been removed.


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

QUESTION TIME

Which has the higher value, the 3rd I.E. of aluminium or the 3rd I.E. of magnesium?Q.1Q.1

CLICK HERE FOR THE ANSWER

QUESTION TIMEQUESTION TIME

Which has the higher value, the 1st I.E. of sodium or the 2nd I.E. of magnesium?Q.2Q.2

CLICK HERE FOR THE ANSWER

QUESTION TIME

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

Which has the higher value, the 3rd I.E. of aluminium or the 3rd I.E. of magnesium?Q.1Q.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)1s2 2s2 2p6 3s1 1s2 2s2 2p6

The 2nd I.E. of magnesium involves the same change in electron configuration…

Mg+(g) Mg2+(g)1s2 2s2 2p6 3s1 1s2 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.

Which has the higher value, the 1st I.E. of sodium or the 2nd I.E. of magnesium?Q.2Q.2

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? CAN YOU DO ALL OF THESE? YES YES NONO

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IONISATION ENERGY