# Hard Chem/Physics Question

1. Sep 29, 2013

### physicsnobrain

1. The problem statement, all variables and given/known data
In the equation for the bohr model of the atom, what is the n value for Li2+ ion?

2. Relevant equations
E = -2.178 x 10^-18J(z^2/n^2)

3. The attempt at a solution

Since it is Li2+ that means it has 1 electron. So z = 1. Now I have an equation with 2 variables (impossible to solve).

I dont know what E is and I have to find n. Does anyone have any idea on how to do this?

2. Sep 29, 2013

### nasu

z is the charge of the nucleus and is not 1 for Li.
For the rest, it may help to post the complete text of the problem.

3. Sep 29, 2013

### physicsnobrain

It's Li2+ not Li. And this is the complete text of the problem.....

4. Sep 29, 2013

### nasu

It does not matter. The charge of the nucleus is 3e for Li, Li+, Li2+.
So z=3.

But n can take any value so the question does not seem to make sense.

5. Sep 30, 2013

### physicsnobrain

IF the question is instead: In the equation for the bohr model of the atom, what is the z value for Li2+ ion?

Does this make more sense?

6. Sep 30, 2013

### Staff: Mentor

Yes.

7. Sep 30, 2013

### physicsnobrain

Well isn't there still three unknown variables Energy and n value and z value?

8. Sep 30, 2013

### Staff: Mentor

But you are not asked to find all three, just to tell what (most likely) Z is.

As worded question doesn't make sense, unless it asks for Z, not n.

9. Sep 30, 2013

### Enigman

What is Z? What does it mean? What is Z for lithium?
(yay! 200th post)

10. Sep 30, 2013

### physicsnobrain

The question exactly as it appears word for word is: In the equation for the Bohr model of the atom, what is the Z value for Li2+ ion?

11. Sep 30, 2013

### Staff: Mentor

You had the right equation in the OP. Go back in your notes/textbook and find what the $Z$ stands for.

12. Sep 30, 2013

### physicsnobrain

it stands for nuclear charge.

13. Sep 30, 2013

### Staff: Mentor

And what is nuclear charge for lithium?

14. Sep 30, 2013

### physicsnobrain

It is +3. So there is no need to use the equation for this problem? Seems more challenging than that.

15. Sep 30, 2013

### Staff: Mentor

No, it is as simple as that. You were making it more difficult than it is from the very beginning.