January 24, 2021, 04:36:05 PM
Forum Rules: Read This Before Posting

### Topic: Calculate Electron Energy  (Read 2165 times)

0 Members and 1 Guest are viewing this topic.

#### Wijdan

• Very New Member
• Posts: 2
• Mole Snacks: +0/-0
• Gender:
##### Calculate Electron Energy
« on: July 30, 2011, 05:15:48 PM »

Calculate the energy of an electron falls from the 5th energy level to the 2nd in Hydrogen atom :

I tried to solve this problem and I got :

but in my book it solved with
n1 = 2
n2 = 5
so the answer is positive (+)
though it loses energy!

Why ?

#### Cavillus

• Regular Member
• Posts: 20
• Mole Snacks: +1/-1
• Gender:
##### Re: Calculate Electron Energy
« Reply #1 on: July 30, 2011, 09:59:23 PM »
Probably, your book considers the promotion of the electron to the 5th level. If the value of the energy is correct, consider the exercise solved
How to Catch a Lion in the Sahara Desert:

The Quantum Measurement Method: We assume that the sex of the lion is _ab initio_ indeterminate. The wave function for the lion is hence a superposition of the gender eigenstate for a lion and that for a lioness. We lay these eigenstates out flat on the ground and orthogonal to each other. Since the (male) lion has a distinctive mane, the measurement of sex can safely be made from a distance, using binoculars. The lion then collapses into one of the eigenstates, which is rolled up and placed inside the cage.

#### fledarmus

• Chemist
• Sr. Member
• Posts: 1676
• Mole Snacks: +203/-28
##### Re: Calculate Electron Energy
« Reply #2 on: August 01, 2011, 09:04:01 AM »
The sign of the answer really depends on the wording of the question, and unfortunately some authors are a little sloppy in the way they word questions. Are they asking for the energy released when an electron falls from the 5th to the 2nd level (which would be positive) or the change in energy of the atom when an electron falls from the 5th to the 2nd level (which would be negative)?

#### Wijdan

• Very New Member
• Posts: 2
• Mole Snacks: +0/-0
• Gender:
##### Re: Calculate Electron Energy
« Reply #3 on: August 01, 2011, 05:49:32 PM »
Probably, your book considers the promotion of the electron to the 5th level. If the value of the energy is correct, consider the exercise solved

I thought so, too
Thank you

=

Quote
The sign of the answer really depends on the wording of the question, and unfortunately some authors are a little sloppy in the way they word questions. Are they asking for the energy released when an electron falls from the 5th to the 2nd level (which would be positive) or the change in energy of the atom when an electron falls from the 5th to the 2nd level (which would be negative)?

Thank you! I got what you've said ..
so if the question is asking for the released energy, we should take into account that n1 < n2 so the value is positive
and if it's asking about the change in energy, so it depends on the problem "5th to 2nd" or "2nd to 5th", right ?
or I can solve it as I did and take the absolute value if it's about the released energy

*actually I committed a mistake when I translated the question, the author is asking about the released energy but I didn't pay attention for it

Thank you very much