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In Bohr model, we know that when an electron in Hydrogen atom goes to a lower orbital it emits some energy which is seen as spectrum.

But my question is Hydrogen has only one electron in one orbital. So how can this electron go to upper or lower orbital when there is only one orbital in Hydrogen and so how can it show any spectrum?

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    $\begingroup$ The hydrogen atom has in infinite number of orbitals. But it has only one electron. The electron can exist in any of those orbitals. $\endgroup$ – garyp Feb 20 '18 at 14:20
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    $\begingroup$ Yes. The energy spacing between the lower-energy states is rather large, but as the energy of the states increases, the spacing gets smaller and smaller, approaching a limit of zero when the energy of the state is zero. There are positive energy states. These are not bound. The electron will "fly away". The energies of these states form a continuum; that is, there is a state arbitrarily close in energy to any other continuum state. $\endgroup$ – garyp Feb 20 '18 at 14:29
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    $\begingroup$ The energy of the bound states of hydrogen can be label by $n$, the principle quantum number. The ground state has $n=1$, the next higher energy state has $n=2$ and so on. The energy of the state $n$ $E_n = -13.6 \mathrm{eV}/n^2$. For any number $n$, as large as you would like, there is a state. $\endgroup$ – garyp Feb 20 '18 at 14:34
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    $\begingroup$ Collision with nucleus: it should. This problem was one of the difficulties that physicists faced at the end of the 19th century. It pointedly demonstrated that the existing theory (Maxwell) was incomplete, and some new ideas (Quantum Mechanics) were needed. $\endgroup$ – garyp Feb 20 '18 at 14:37
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    $\begingroup$ @Asif While it is true that there are an infinite number of possible states for the electron, the energy spectrum is bounded. As other users have commented, $E_n = -\frac{13.6}{n^2} eV$ where $n \geq 1$. Thus, $-13.6 eV \leq E_n \leq 0$, and if more than $13.6 eV$ energy is gained by the (ground state) electron in hydrogen, it will no longer be bound to the atom and the atom will be ionised. $\endgroup$ – Styg Feb 21 '18 at 10:25
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The Bohr model does not limit the number of possible orbitals that hydrogen has. At any given time, the single electron is in any one of the possible orbits, sure. But there is no restriction on which orbit it can be in.

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  • $\begingroup$ Can you please describe yourself in equations? $\endgroup$ – Theoretical Feb 20 '18 at 14:26
  • $\begingroup$ I'm not sure I can express in equations the fact that all the Bohr orbits are valid states (with different energies) for the electron to be in. $\endgroup$ – Styg Feb 20 '18 at 14:29
  • $\begingroup$ @AsifIqubal The binding energy of an electron in hydrogen expressed in electronvolt is $E_b = 13.6/n^2$ where $n = 1, 2, 3...$ There is no limit to the principal quantum number $n$. $\endgroup$ – Pieter Feb 20 '18 at 14:32

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