Ionisation Energy

teaspoon

Can someone tell me how you work out the group an element belongs to by looking at the ionisation energies.

For example:-
736, 1451, 7740, 10500, 13600
This element is in group 2 but how do you work it out?

There is a very large increase between the second and third ionisation energies, indicating that the third (fourth, fifth etc.) electrons are held far more tightly by the nuclear charge than the first two (ie. that the first two were s-block electrons and the next few come from a different, much lower, energy level).

Ben

Reply 2

Basically, you just look at the significant jumps and decide, gven what you know about the block system, what group best fits the data. Very large jumps in I.E. are often due to a change in shell, smaller jumps are due to a change in subshell (other jumps can be a bit odd).

Ben

Reply 3

Ralfskini

I would have thought the next few would come from a higher energy level.

The lower the energy, the more required to remove it to infinity - that's ionisation. Closer to the nucleus mean lower energy.

Ben

Nicely deleted, by the way - too late!

Reply 4

elpaw

15

a better way of deciding what the "significant" jumps are is to plot the numbers (probably logarithmically); its easier to see the jumps than to deduce them by staring at some numbers

Reply 5

OP

can you explain how you would know its in group 2?

Reply 6

teaspoon

can you explain how you would know its in group 2?

There is a very large difference between the second and third ionisation energies - indicating that the electrons being removed in each case are in different shells. You can deduce from this that the first two electrons removed were in 's' orbitals and the third came from a 'p' orbital in the next lowest energy shell. Hence (almost), the element is in group 2.

Ben

Reply 7

OP

Thank you for your replies Ben. Can you give me a couple of examples so i can try some.

Reply 8

teaspoon

Thank you for your replies Ben. Can you give me a couple of examples so i can try some.

I can't give examples, because I don't have numerical data. Sorry!

Ben

Reply 9

OP

So to summarise about ionisation energy, the important is to look where the jump is from the first ionisation energy?

Reply 10

teaspoon

So to summarise about ionisation energy, the important is to look where the jump is from the first ionisation energy?

To look at all the jumps and see if you can fit any trends you see with the graph of ionisation energies (the zig-zag thing from AS module 1) - that will help you decide on a suitable group. If you learn the shape of the graph, you should be fine.

Ben

Reply 11

OP

thanks for all your help.

Reply 12

OP

ok i've found a couple of questions can somebody check them if they're correct?

1. An element has the following successive ionisation energies (KJmol-1)

577, 1980, 2960, 6190, 8700, 11400.
Is this element in group 3 because there is a big jump between the 3rd and 4th ionisation energy?

2.
A - 502 560 6918
B - 748 1463 7741
C - 558 1827 2579
D - 1003 2261 3423
E - 422 3060 4431
Which element is most likely to form M+ ions in the gas phase?
I think it is element E because there is a jump between the 1st and 2nd ionisation energy..

Are they correct?

Reply 13

teaspoon

ok i've found a couple of questions can somebody check them if they're correct?

1. An element has the following successive ionisation energies (KJmol-1)

577, 1980, 2960, 6190, 8700, 11400.
Is this element in group 3 because there is a big jump between the 3rd and 4th ionisation energy?

2.
A - 502 560 6918
B - 748 1463 7741
C - 558 1827 2579
D - 1003 2261 3423
E - 422 3060 4431
Which element is most likely to form M+ ions in the gas phase?
I think it is element E because there is a jump between the 1st and 2nd ionisation energy..

Are they correct?

I agree with you on both counts.

Ben

Reply 14

Christophicus

18

teaspoon

ok i've found a couple of questions can somebody check them if they're correct?

1. An element has the following successive ionisation energies (KJmol-1)

577, 1980, 2960, 6190, 8700, 11400.
Is this element in group 3 because there is a big jump between the 3rd and 4th ionisation energy?

2.
A - 502 560 6918
B - 748 1463 7741
C - 558 1827 2579
D - 1003 2261 3423
E - 422 3060 4431
Which element is most likely to form M+ ions in the gas phase?
I think it is element E because there is a jump between the 1st and 2nd ionisation energy..

Are they correct?

Yes I agree.

Reply 15