CBSE Class 12-science Answered

When Hydrogen is excited it emits light as photons de-excite. Or conversely, the Hydrogen will absorb photons of certain energies. The strength of the line from a source of Hydrogen will depend on how many electrons are in a particular excited state. If only very few electrons are the first excited state, the Balmer lines will be very weak. If many Hydrogen atoms are in the first excited state then the Balmer lines will be strong.

When an electron absorbs a photon it gains the energy of the photon. Because an electron bound to an atom can only have certain energies the electron can only absorb photons of certain energies. For example an electron in the ground state has an energy of -13.6 eV. The second energy level is -3.4 eV. Thus it would take E₂ − E₁ = -3.4 eV − -13.6 eV = 10.2 eV to excite the electron from the ground state to the first excited state.

If a photon has more energy than the binding energy of the electron then the photon will free the electron from the atom – ionizing it. The ground state is the most bound state and therefore takes the most energy to ionize.

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