Emission spectrum lines of hydrogen

[Entanglement]

I was told at school that when a hydrogen electron gains heat energy enough to excite it shifts to a higher energy level, then after a very small period it falls back to its ground energy level, that means all the energy it gains should be lost, but if that is true since hydrogen has an electron at the first energy level, why when it's excited it doesn't have to fall back to its original energy level, but instead it falls to any Lower energy level producing different series of spectrum, thanks in advance guys !

 

[Drakkith]

A full understanding would have to involve Quantum Mechanical rules, but the short version is that the electron simply has a probability of falling from one energy level into any of the lower ones. I'm not sure that answers your question, and if not, perhaps someone more knowledgeable with QM can answer you.

 

[Khashishi]

Some fraction (possibly 0) of the excited hydrogen atoms will decay directly to the ground state, and some fraction will take multiple steps to go to the ground state. It depends on the branching factors of the transitions, which is calculated from the transition probabilities.

You can look at this grotrian diagram to see some of the allowed transitions
https://en.wikipedia.org/wiki/File:Grotrian_H.svg
Generally speaking, from a starting state, the bigger jumps downward are more likely than than the smaller jumps, so if you start from the 3p state, most of them will jump directly to the 1s state, but some will jump to the 2s state (which is metastable). On the other hand, if you start from the 3d state, all of them will jump to the 2p state because transition to the ground state is not allowed.