# Ionization energy - compare 2 unknown elements and decide their group

1. Apr 21, 2012

### carle

Hello. I have a question about ionization energy:

Two hypothetical elements in the 2nd or 3rd period have the following ionization energies:

Element X
First: 800 kJ/mol
Second: 2500 kJ/mol
Third: 3900 kJ/mol
Fourth: 23000 kJ/mol

Element Y
First: 700 kJ/mol
Second: 2200 kJ/mol
Third: 3500 kJ/mol
Fourth: 19000 kJ/mol

To what group in the periodic table should element X be in, and what charge should the ion in element X have?

The answer is group 13 and charge +3. How could you possibly know this? I can see that the fourth energy level is far more than the third, so it should be somewhere between group 13-17, but how do you know which one?

2. Apr 21, 2012

### Staff: Mentor

Why is the fourth much larger? What does it tell you about electrons being removed?

3. Apr 21, 2012

### carle

Well, is it because the first three energy levels remove all the group 13 valence electrons, and then you need much more energy to remove one more electron? But wouldn't it require much energy to remove the last valence electron in any element, so why can't it be for example group 14 loosing 4 valence electrons?

4. Apr 21, 2012

### Staff: Mentor

How many valence electrons in group 14?

5. Apr 21, 2012

### carle

4. Which tells me.. ?

6. Apr 21, 2012

### Staff: Mentor

What is a difference between valence electrons and other electrons? Which are easier, which are harder to remove?

7. Apr 21, 2012

### carle

I'm sorry, but this leads me nowhere, so I'll be better off if someone simply could give me an explanation of why it is group 13.

8. Apr 21, 2012

### Staff: Mentor

Don't give up so easily.

Try to answer the questions I asked. You DO know what are valence electrons? What definition do you know? Why are they called "valence"?

9. Apr 21, 2012

### carle

Yes, I know what valence electrons are; the electrons in an atoms outer shell.

Group 13 elements have 3 valence electrons. Then I figure that in the first, second and third ionization energy levels you have removed 1, 2 and 3 of the group 13 valence electrons, so that there are no valence electrons left. In the fourth level, you are removing an additional electron. Is it this "jump" from the outer shell to the inner that requires much more energy?

10. Apr 21, 2012

### Staff: Mentor

Exactly! Valence electrons are taking part in binding because they are not so tightly bounded to the nucleus. They can be removed much easier than other electrons, and their ionization energies are smaller.