Why is Bohr's model of an atom limited to explaining only the hydrogen spectrum?

  • Context: Undergrad 
  • Thread starter Thread starter kay
  • Start date Start date
  • Tags Tags
    Atom Model
Click For Summary

Discussion Overview

The discussion centers on the limitations of Bohr's model of the atom, particularly its inability to explain the spectra of atoms other than hydrogen. Participants explore the implications of having multiple electrons in atoms and consider specific examples, including isoelectronic species.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant questions why Bohr's model cannot explain the spectrum of atoms other than hydrogen and asks for examples.
  • Another participant suggests that the presence of multiple electrons in atoms is not accounted for in the Bohr model.
  • A participant notes that Bohr's model provides a reasonable approximation for light atoms with a single electron but fails for heavier atoms due to relativistic effects and nuclear size.
  • There is a mention of calculating orbital speed for a U91+ ion using non-relativistic mechanics, raising questions about relativistic effects.
  • Some participants express confusion about the concepts of orbital speed and relativistic mechanics, indicating a lack of familiarity with these topics.
  • One participant emphasizes that while Bohr's orbits have a defined speed, classical mechanics becomes inaccurate at speeds approaching that of light, necessitating the use of relativistic equations.
  • Another participant suggests studying quantum numbers assigned to electrons to better understand the limitations of Bohr's theory, which was initially based on Planck's law and hydrogen spectrum observations.

Areas of Agreement / Disagreement

Participants express varying levels of understanding regarding the implications of Bohr's model, with some agreeing on its limitations for multi-electron atoms while others remain uncertain about specific concepts like relativistic effects and orbital speed. The discussion does not reach a consensus on the broader applicability of Bohr's model.

Contextual Notes

Participants highlight limitations in understanding relativistic effects and the concept of orbital speed, indicating that some foundational knowledge may be missing. The discussion reflects a range of familiarity with the underlying physics and mathematics.

kay
Messages
60
Reaction score
2
Why is Bohr's model of an atom not able to explain the spectrum of atoms other than hydrogen? Can you give an example? :what:
 
Physics news on Phys.org
Is that homework?

Here is a hint: other atoms have more than one electron. Is this taken into account in the Bohr model?
 
No, it isn't. While reading the chapter i encountered this line which says that Bohr's model can't explain the spectrum of atoms other than hydrogen.
But another doubt, can Bohr's model explain the spectrum of species isoelectronic to Hydrogen?
 
The Bohr model gives a reasonable approximation for light atoms (not molecules!) with just a single electron, yes.
It does not work well for heavy atoms due to relativistic effects and the size of their nuclei.
 
Relativistic effects? :/
 
Imagine a uranium nucleus with one electron, i.e. a U91+ ion. Calculate the orbital speed in the first Bohr orbit, assuming non-relativistic mechanics.
 
I'm a student of 11th class. I have no idea. I don't even know orbitals had speed.
I don't know what is relativistic or anything. Sorry. I can't understand anything. :(
 
Sorry, I thought you had at least seen a derivation of the Bohr orbit radii, which includes the orbital speed along the way. If you haven't, try the Wikipedia article on the Bohr model. It has enough information that you should be able to get the electron speed in orbit "n" with only a little bit of algebra.

The boundary between "non-relativistic" and "relativistic" is not sharp, but a common rule of thumb is that if a speed is greater than 0.1c, you really should be using relativistic equations.
 
Last edited:
kay said:
I don't even know orbitals had speed.
They do not, but Bohr's orbits have a speed.

If that speed gets comparable to the speed of light ("c"), the formulas from classical mechanics (like kinetic energy = ##\frac{1}{2}m v^2##) get imprecise to outright wrong and you have to consider special relativity.
 
  • #10
You should first do study of different quantum numbers assigned to electrons in an atom,Bohrs theory was succesfu l in expaining hydrogen spectra at that time,but it was a rudimentary theory made out of Plancks law and observation of hydrogen spectra.
 

Similar threads

Undergrad Instantaneous dipole moment and orbitals
  • · Replies 2 ·
Replies
2
Views
1K
Undergrad Why do only low-pressure gases emit a line spectrum?
  • · Replies 6 ·
Replies
6
Views
3K
Undergrad Why does a hydrogen gas tube produce a hydrogen atomic spectrum?
  • · Replies 9 ·
Replies
9
Views
2K
Undergrad Question about the Bohr model of atom and and electron in an orbital
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Why are the spectral lines weak in my hydrogen Geissler tube?
  • · Replies 8 ·
Replies
8
Views
2K
Graduate How to obtain the spectrum for a given atom or simple molecule?
  • · Replies 10 ·
Replies
10
Views
4K
High School How does the hydrogen line spectrum work with only one orbit?
  • · Replies 10 ·
Replies
10
Views
3K
Graduate Does the Bohr model go against classical Electromagnetism
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Relevance of the Rydberg Constant?
  • · Replies 25 ·
Replies
25
Views
8K
Undergrad Source of the damping force in Lorentz model
  • · Replies 1 ·
Replies
1
Views
2K