# Hard Chem/Physics Question

physicsnobrain

## Homework Statement

In the equation for the bohr model of the atom, what is the n value for Li2+ ion?

## Homework Equations

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

## 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?

## Answers and Replies

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.

physicsnobrain
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.

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

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.

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?

Mentor
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?
Yes.

physicsnobrain
Yes.

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

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.

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

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

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?

I am still unsure of how to go about this question. Which equation should I use?

Mentor
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?

I am still unsure of how to go about this question. Which equation should I use?
You had the right equation in the OP. Go back in your notes/textbook and find what the ##Z## stands for.

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

it stands for nuclear charge.

Mentor
And what is nuclear charge for lithium?

physicsnobrain
And what is nuclear charge for lithium?

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

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