Can someone please check this to see if it is correct? It's for an assignment
In 1913, Danish physicist Niels Bohr solved this problem, by proposing yet another model of the atom. In this model, electrons would be restricted to orbiting in atomic shells. As the electron orbited around the nucleus, it would eventually lose energy, due to attraction, and would move to a lower energy state i.e. an atomic shell closer to the nucleus. Eventually, when the electron reached the lowest possible energy state, it would give off a photon and return to a higher energy state, further away from the nucleus.
I don't quite know why or how the electron returns to its higher energy state, hope someone can explain to me. No fancy formulae please. This is just the start of my chemistry unit so all I know so far is just from self-research. Thanks
Where ever it came from, it is incorrect.
Bohr proposed that the electrons circled the nucleus in semi-stable states. That is to say if an atom is in an excited state the electron could give off a photon, but would have to give off energies of only certain amounts; the electron would be required to "jump" down the energy scale in "quanta" of energy until it reached a lowest, or "ground" state. There is nothing to say that an electron in the ground state will get re-elevated to an excited state again.
This was a radical idea since Maxwell's equations proved that a charge moving in a circle will continuously give off electromagnetic radiation and spiral into the center. Bohr's electrons didn't do that. They emitted energy if in an excited state and "spiraled" in to a lowest state, but they stayed in that lowest state and didn't spiral in any further. It was a completely preposterous model given the state of Science at the time, but couldn't be discarded since it worked to an extremely good approximation.
(By the way, Bohr's model of the atom was in his PhD dissertation. His mentors had assigned him the "impossible" problem of explaining line spectra to embarrass him and show him how much more he had to learn about science. He was, in fact, completely wrong. But since his results were so accurate nobody could explain that he was wrong until Schrodinger (and others) solved the wave equation for Hydrogen in the late 1920s. And the model still remains very useful today to introduce the topic of atomic spectra and atomic orbitals. Guess his mentors showed him, didn't they? )
Thanks... so the Bohr Model still hadn't solved the spiralling in of electrons, it was just 'better' than the Rutherford Model in that it was more accurate. I thought it seemed a bit odd that the electron doesn't fall lower than ground state.
How does this link in with Pauli's exclusion principle though (or isn't it supposed to)? i.e. An electron falls to the ground state, and the atom doesn't receive any energy. After a while, the other electrons in their orbits also lose energy and fall to ground state. Wouldn't that result in multiple electrons in the same atomic shell?
It was later taken as a postulate of quantum mechanics that no two fermions (half-integer spins) could share the same quantum numbers (this is the Pauli exclusion principle), but any number of bosons (integer spins) could have the same quantum numbers. This was eventually proven using a statistical version of quantum mechanics. No particles have ever been found that are neither fermions nor bosons.
It is the other way around. An electron is excited and aquires more energy it goes to a higher shell. At a later time it can fall back to it's original lower energy shell and gives off a photon.The emmision of a photon balances the energy equation and the energy of the photon is the same as the difference in potential energy between the two shells.
The electron can only exist in the shells and not between them so it "quantum leeps" from one shell to another. This means electrons in an atom can only absorb or give of energy (photons) in whole "quantum chunks". Look up Planck's constant and Einstiens photoelectric experiment to learn more about this stuff. Then again you might not want to go there.