Here is a little quantummechanics which shows you how an electron jumps between different energy levels. More can be found in the section Physics/atom_physics




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The first thing you need to know is the general picture of matter. Here it is in short. Matter consists on a microspic level of molecules, which are small conglomerates of different types of atoms. For example alcohol consist of small alcohol molecules, which consist of atoms in the combination C2H5OH, which means that one molecule of alcohol consists of 2 carbon atoms, 5 hydrogen atoms and 1 oxygen atom. It schematically looks like this.



So that's what really inside this.



As you can see in the picture molecules themselves are made of smaller particles, so called atoms. We have helium atoms, hydrogen atoms and about a 108 or so more. They are called elements and you can check them out in a so called "periodic table of the elements". Atoms themselves are again build of many smaller particles. (One can't really call an atom or molecule a particle since they are build out of many different "things" themselves, but since they are so small one can't even see them with the bare eye, we call even a molecule a particle as if it were one solid object.) In the center of an atom is a blob, usually referred to as the "core", surrounded by a cloud of electrons. (the size of the cloud depends on which element we're talking about, but look in Physics/atom_physics for info on that.) The important thing is that those electrons according to quantum theory are moving in certain orbits. The exact physics behind it won't be discussed here, but the important thing is that the electrons can change position between certain orbits. They can normally not do that themselves, but they can be forced to move from one orbit to another, for example by a passing photon. Every orbit represents a certain amount of energy. So between two orbits there is a certain amount of energy-difference. When a photon interacts with an electron and by doing so delivers the exact amount of energy to the electron to move from it's orbit to an orbit with a higher energy, the photon will be absorbed. Since systems want to be in a state where the energy is as low as possible, the electron will fall back again after a certain amount of time. While it does this, it will release it's gained energy in the form of another photon. An example of the orbits of electrons is given in this picture.



As you can see every transition between two orbits gives a certain color. This explains the absorption lines and the emmission lines mentioned in the text about "line-formation". The n you see in the picture stands for the orbit the electron is in and is one of the quantummechanical "main-tags" to describe things. The higher the number the further away the orbit is from the positive core shown in the center of the orbits and the higher the energy of the electron in an orbit. In fact what very few people know is that the "n" wasn't really introduced to "tag" the energy, but rather to "tag" the angular momentum of the electron in it's orbit. Bohr DIDN'T start with dividing the energy of the electrons in quanta, but he quantisized the specific angular momentum of the electrons in their orbits. (If you want to know what angular momentum is, it's explained in /physics/angular_momentum.) So, higher orbits have higher energies, but essentially have higher orbital angular momenta! This is enough for now. More things about the physics of the atom can be read in /physics/atom_physics. (soon enough)