Simulation · Physics · Class 12
Electrons into hydrogen: which lines light up?
From the lesson Energy levels in Atoms. Change the values and watch what happens.
Electrons into hydrogen: which lines light up?Physics · Class 12
The idea behind it
NCERT §12.4.1
- The atom's energy is lowest (most negative) with the electron in the innermost orbit, n = 1. For n = 2, 3, … the magnitude of E shrinks, so the energy rises in the outer orbits.
- The lowest state is the ground state: n = 1, orbit radius a₀, E₁ = −13.6 eV. The least energy that frees the electron from the ground state, 13.6 eV, is the ionisation energy of hydrogen, and Bohr's prediction agrees very well with experiment.
- At room temperature most hydrogen atoms are in the ground state. Energy from collisions (for example with electrons) can lift the electron to a higher level: the atom is then in an excited state.
- E₂ = −3.40 eV, so excitation to the first excited state needs E₂ − E₁ = 10.2 eV. E₃ = −1.51 eV, so the second excited state (n = 3) needs 12.09 eV.
- From an excited state the electron can fall back to a lower level, emitting a photon. The higher the excitation (the larger n), the less energy is needed to free the electron.
- Fig. 12.7 stacks the levels as horizontal lines, numbered by n from the bottom up in order of rising energy. The top, n = ∞, has E = 0: the electron removed to infinity and at rest. The levels crowd closer together as n increases.
- Above E = 0 the electron is free and can have any energy: a continuum of states.