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Hydrogen Spectrum

The hydrogen atom contains only one electron in the first orbit (K shell). This is the normal orbit or ground state and represents the stationary state of the unexcited atom. Energy may be absorbed by this electron, which is then raised from its normal orbit to a higher energy level. In this new level, the electron possesses more energy and is less stable than before. It will, therefore, fall toward the nucleus until it reaches either the normal orbit or some intermediate level. In this process, energy is released as a photon of frequency, E = .
Spectral lines are produced by radiation of photons, and the position of the lines on the spectrum is determined by the frequency of photons emitted. Transition to innermost level (n = 1) from higher levels (n = 1, 3, 4, etc.) gives the first, second, third, etc., line of the Lyman series as in the below figure. 
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Hydrogen atom contains only one electron, but its spectrum consists of several lines. Why? A sample of hydrogen contains a very large number of atoms. When energy is supplied, the electrons present in different atoms may be excited to different energy level. These electrons when they fall back to various lower levels emit radiations of different frequencies. Each electronic transition produces a spectral line. Energy is absorbed by an atom when an electron moves from the inner energy level to the outer energy level. The amount of energy necessary to remove an electron from its lowest level (n = 1) to infinite distance resulting in the formation of a free ion is called the ionization potential. The ionization energy of hydrogen is 2.18 × 10–18 J or 13.595 eV (1 eV = 1.602 × 10–19 J).
If an electron acquires more than enough energy to permit its removal from the atom, the extra energy is carried off by the free electron as kinetic energy. Because of the very small magnitude of the quanta of translational (i.e., kinetic) energy, this energy is essentially continuously variable. The spectrum beyond the series limit thus appears continuous. From the position of continuum, we may calculate the ionization potential.

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