# Why do electrons jump between orbitals? [duplicate]

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When an electron is excited to higher energy levels, it will jump back to the same level from which it was excited. Why does it develop "sentiment" with that level?

## marked as duplicate by ACuriousMind♦, mpv, Ruslan, user36790, GertFeb 3 '16 at 0:30

• Systems like to reach a lower energy state. Whether they do and how long it takes depends on many factors. Electrons in some energy levels like to stay in those levels longer than in other energy levels. – Farcher Feb 2 '16 at 15:44
• That is what my question is. Why do they "like" to stay in those orbitals? – siva phanindra Daggubati Feb 2 '16 at 15:47
• Possible duplicate of Quantum mechanics scattering theory – ACuriousMind Feb 2 '16 at 15:47
• It will not always jump back down to the same level. It has no 'sentiment'. But, given that it could jump up to a level does mean that it has some reasonable overlap integral to jump back down to that level, which some other electrons might not given their different quantum numbers. – Jon Custer Feb 2 '16 at 15:50
• Energy levels are like hills. Higher energy means steeper hill, harder to get up. Lower energy, means flatter hill, easy to get up. Electrons move randomly, so they would find it harder to climb up to higher hills, and easy to fall off of them. – Zach466920 Feb 2 '16 at 16:07

This is the hydrogen atom energy level solutions, as an easy example.

The electron sits at the ground state, and can be kicked up to an excited state by the appropriate photon i.e. given that the photon has the quantized energy needed. For each energy level one can calculate using the solutions of the Schrodinger equation, the probability for the electron to fall down to one of the lower energy levels, releasing a photon with the energy difference. It does not have to be the ground state, there could be cascades. This happens because the potential is attractive. If it were not for the quantization of the energy levels, the electron would radiate continuously and would fall into the proton and become a neutron. Quantization assures the stability, but still the attractive force ensures that there is a high probability of filling lower energy states, and rest at the ground state.

In complicated atoms and molecules the quantum numbers of the states become important and the probabilities of decay may depend on angular momentum states and spin states etc ( including the Pauli exclusion principle, quantum mechanics needs to be studied in depth to really understand the subject)

I don't know if I'm understanding your question right, but I think you are trying to pose a deeper question than it might seem at first sight... In ordinary quantum mechanics, when you study the hydrogen atom, you derive a set of solutions for the electron wavefunction using the Schrödinger equation (with different values of the energy). These are the different orbitals in which the electron can live.

Now, in principle, these states are stationary, i.e., once you place an electron in an orbital, say the one defined by the quantum numbers $n=2$, $l=1$, $m=0$; the wavefunction does not change with time (technically, only its modulus squared is constant, but that's only a small detail since the energy remains the same), so basically the electron never returns to the ground state according to this theory. Obviously this must be wrong since we know that the electron does return to the ground state (or at least to a state with lower energy), and quite fast. The key point here is that the hydrogen atom is not an isolated system: even in vacuum, when you consider the electromagnetic field from a quantum field theory point of view you get that this vacuum field in some sense interacts with the hydrogen atom, causing the electron to decay to a lower energy state. I'm not an expert in these matters, so I won't try to explain in detail what this means basically because I have never worked out exactly how the process goes (maybe somebody else could develop this point?), but you can read something more here:

https://en.wikipedia.org/wiki/Spontaneous_emission#Theory

The statement in the question is not fully correct. When an electron in a system is excited from a lower to a higher energy level the system becomes excited. That is to say, system reaches to a state which is not favourable. This is an unfavourable state for the system because the excited electron leaves a hole behind.

There are several different mechanisms for the system to relax. The "drop" of the initially excited electron back to its original level is just one of the options. Some other electron can actually fill the hole by emitting a photon with suitable energy. The system can emit an Auger electron. If the system is a molecule it can even dissociate. The probability for these different relaxation "channels" can be calculated.

• Neil degrasse Tyson, popular astrophysicist mentioned this jumping of electrons in his cosmos documentary.He simply says "we don't know the reason why electrons jump back from their excited states" .As for the answer of linuxick, the word "not favorable" is ambiguous.what is 'not favorable' from the atom's point of view? – siva phanindra Daggubati Feb 2 '16 at 16:52

An electron in a higher energy orbital does not necessarily decay directly into the ground state. If an electron in a hydrogen atom is excited into, say, the $n=4$ energy level, all of the following are possible decay paths:

• $4 \rightarrow 3 \rightarrow 2 \rightarrow 1$
• $4 \rightarrow 3 \rightarrow 1$
• $4 \rightarrow 2 \rightarrow 1$
• $4 \rightarrow 1$

Each of these decay paths release a number of photons equal to the number of arrows. In fact, the helium-neon (HeNe) laser uses the $n=3 \rightarrow n=2$ transistion of neon to emit light.