When hydrogen atom excites from ground state what happens to its kinetic and potential energies?

1 Answer
Jun 13, 2018

Well, as the electron in the hydrogen atom gets excited, energy put into it that causes such an excitation (e.g. a laser!) transforms into kinetic energy #K# that allows the electron to overcome some of the potential energy of attraction #V# that the nucleus enforces.

https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Quantum_Mechanics/

The higher the electron gets in energy, the more these energies balance out, i.e.

#overbrace(K)^"Used to excite" + overbrace(V)^"Holds electron in atom" >= V#

where #V = -e^2/(4piepsilon_0r) < 0# is the coulombic potential energy enforced by the hydrogen atom nucleus interacting with the electron. Here, #K# can be greater than #V#.

Now suppose you add energy until you ionize the atom.

https://ecee.colorado.edu/~bart/book/

The electron starts as the #color(red)("red")# wave shown above.

The more energy you put into exciting the atom, the larger #K# is, until it reaches #K_max = V# (the #color(lightgreen)("green")# wave is almost there).

When #K > V# (as in the #color(blue)("blue")# wave), the electron escapes with some excess kinetic energy #K_"xs"# (in that case, define #K = K_max + K_"xs"#), while the required kinetic energy to escape #K_max = DeltaH_"IE"# is known as the ionization energy:

#K_"xs" = overbrace(K)^"Used to ionize atom" + overbrace(V)^"Holds electron in atom" >= 0#

And in that case, this resembles what is known from the photoelectric effect:

https://physics.info/photoelectric/

#K_"xs" = hnu - phi >= 0#

where #hnu# is the incoming light energy and #phi# is the threshold energy #hnu_0#, or the work function.

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