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Total potential energy

Zenarthra

For example, in an electron in an energy level.
Is the Total PE = EPE + KE at any distance from the nucleus?

Thanks!

Reply 1

Stonebridge

Original post by Zenarthra

For example, in an electron in an energy level.
Is the Total PE = EPE + KE at any distance from the nucleus?

Thanks!

I think you mean
Total energy = EPE + KE

If so the answer is yes.

Reply 2

Zenarthra

Original post by Stonebridge

I think you mean
Total energy = EPE + KE

If so the answer is yes.

Would this be a correct explanation of why sub shells further out have more energy?
Set PE=0 at infinity
Electrostatic PE of electron and nucleus = - kQq/r
As r-> infinty EPE -> 0
So that sublevels further out have lower EPE.
KE at closer sublevels is < KE at further sublevels
So that n=1 has EPE and KE1
If a photon excites an electron, it absorbs energy E=hf.
So that at n=2 it has lower EPE but greater KE (KE1 + hf)
So the Total energy at sub levels further out is greater due to greater increase in KE at further sub levels.
TE = KE + EPE

Would this be correct or..?

Thanks!

Reply 3

Stonebridge

Original post by Zenarthra

Would this be a correct explanation of why sub shells further out have more energy?
Set PE=0 at infinity
Electrostatic PE of electron and nucleus = - kQq/r
As r-> infinty EPE -> 0

Correct up to this point.

So that sublevels further out have lower EPE.

No. More EPE. If the EPE is negative inside the atom, it gets greater as you move out because it's zero at infinity.
Zero is greater than a minus value.

KE at closer sublevels is < KE at further sublevels

No. The electron has zero EPE and zero KE when it is free outside the atom.
Inside the atom it has negative EPE, and positive KE because it is moving. (This is the Bohr Model.)
The maths, which is complicated, shows that the total energy (EPE + KE) is actually negative inside the atom. This is because the EPE is more negative than the positive part due to KE.

Reply 4

RoyalBlue7

Original post by Stonebridge

I think you mean
Total energy = EPE + KE

If so the answer is yes.

What about GPE?

Posted from TSR Mobile

Reply 5

Stonebridge

Original post by RoyalBlue7

What about GPE?

Posted from TSR Mobile

What about it?
Have you worked out the GPE of an electron in a hydrogen atom? (And compared it with the EPE?)

If not, doing so will answer your question.

Reply 6

Zenarthra

Original post by Stonebridge

Correct up to this point.

No. More EPE. If the EPE is negative inside the atom, it gets greater as you move out because it's zero at infinity.
Zero is greater than a minus value.

No. The electron has zero EPE and zero KE when it is free outside the atom.
Inside the atom it has negative EPE, and positive KE because it is moving. (This is the Bohr Model.)
The maths, which is complicated, shows that the total energy (EPE + KE) is actually negative inside the atom. This is because the EPE is more negative than the positive part due to KE.

Ok thank you, so Total energy becomes more positive as n-> (infinity/whatever number) and this is why sublevels further away have higher energy than sub levels closer?

Reply 7

Stonebridge

Original post by Zenarthra

Ok thank you, so Total energy becomes more positive as n-> (infinity/whatever number) and this is why sublevels further away have higher energy than sub levels closer?