Derivation of formula for orbital ranges in hydrogen atom

In summary, the conversation discusses the calculation of the radius of an atom using the principles of angular momentum and centripetal force. The formula for the radius is derived using the electron mass, velocity, angular momentum, and the Coulomb force between the proton and electron. However, a minor flaw is found in the formula, as the radius decreases with higher values of n. The correct formula is the reciprocal of the original equation. The conversation concludes with the request for someone to identify the error and offer clarification if needed.
  • #1
jjr
51
1
I almost have the answer, I'm sure there's just a minor flaw in my reasoning. Here it goes:
We're given that the angular momentum of the atom is integer multiples of h-bar (n[itex]\hbar[/itex]) (integer depending on the orbit). Now the centripetal force is given by F = [itex]\frac{mv^2}{r}[/itex] = [itex]\frac{p^2}{mr}[/itex] = n^2[itex]\hbar[/itex]^2/mr where m is the electron mass, v is the velocity, p is the angular momentum and r is the range. This force equals the attractive coloumb force between the proton and electron, so: [itex]\frac{p^2}{mr}[/itex] = [itex]\frac{k(q^2)}{r^2}[/itex] => r = k(q^2)m/(n^2[itex]\hbar[/itex]^2) where k is coulombs constant, q is the charge of electron/proton.

The problem is obvious, seeing as how the radius drops with higher n's. The answer is in fact the reciprocal of the right part of the last equation. Can anyone spot my error?

Thanks, J
 
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  • #2
Bump. If something is confusing, I'll be happy to elaborate
 
  • #3
p=mv is linear momentum, not angular momentum.
 

1. What is the derivation of the formula for orbital ranges in a hydrogen atom?

The formula for orbital ranges in a hydrogen atom is derived from the Bohr model of the atom, which states that electrons orbit the nucleus in circular orbits with quantized energy levels. This model also takes into account the Coulombic force between the positively charged nucleus and the negatively charged electron.

2. How is the Coulombic force involved in the derivation?

The Coulombic force, which is the electrostatic force between two charged particles, is used to determine the centripetal force that keeps the electron in orbit around the nucleus. This force is equal to the force of gravity in the classical model of the solar system, but instead of being dependent on mass, it is dependent on the charges of the particles.

3. What is the significance of the Rydberg constant in the formula?

The Rydberg constant, denoted by R, is a fundamental constant in physics that is used to calculate the energy levels of a hydrogen atom. It is involved in the formula for orbital ranges because it represents the proportionality between the energy levels and the inverse of the square of the orbital radius.

4. Are there any simplifications made in the derivation?

Yes, the derivation of the formula for orbital ranges in a hydrogen atom assumes that the nucleus is stationary and that the electron is in a circular orbit. It also uses classical mechanics rather than quantum mechanics, which provides a more accurate description of the atom's behavior.

5. How is this formula applied in other atoms or molecules?

This formula can be applied to other atoms or molecules by replacing the mass and charge of the electron and nucleus with the corresponding values for the specific atom or molecule. However, it should be noted that this model is only accurate for single-electron systems, and more complex models are needed for multi-electron atoms or molecules.

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