My teacher said that if we irradiate the metal strip (used in generating the photoelectric effect) with light having frequency equal to the metal's threshold frequency, then the electrons will have enough energy to ionize and get separated from the metal atoms. However, they won't have any kinetic energy left, and so will remain stationary.enter image description here

But why does it matter that the electrons won't have any kinetic energy? Shouldn't the electrons get repelled from the electrons behind them and go forward?

  • $\begingroup$ BTW, Einstein got for the photoelectric effect (officially mainly for that, to avoid SR/GR critics) his Nobel price in physics, not chemistry. $\endgroup$
    – Poutnik
    Commented Aug 15, 2022 at 9:06
  • $\begingroup$ @Poutnik do we assume all the electrons that have been removed from the atom to be near stationary? $\endgroup$ Commented Aug 15, 2022 at 9:43
  • $\begingroup$ @Poutnik And why do those near-stationary electrons attach themselves to the matrix instead of getting repelled ahead? $\endgroup$ Commented Aug 15, 2022 at 9:53
  • $\begingroup$ Also, should I delete this question and post it again at the physics stack exchange? $\endgroup$ Commented Aug 15, 2022 at 9:54
  • $\begingroup$ @Poutnik so as far as I have understood, the reason behind the electrons not being repelled ahead is that they have a higher tendency to form anions. Am i correct? $\endgroup$ Commented Aug 15, 2022 at 15:49

1 Answer 1


Electrons have always some kinetic energy, it is requirement of QM principles. Plus there is distribution of the threshold photon energy due Doppler effect, because of moving atoms. Near stationary electrons will probably attach themselves back to the solid matrix, possibly leading to local charge disbalance. We are already used to that in static electricity context.

In the above scenario, electron will have like thermal speed when released. what for low electron mass and 298 K is typically $v_\mathrm{RMS}=\sqrt(\frac{3kT}{m_\mathrm{e}}) \approx \pu{116 km/s}$.

For mettallic conductors with metallic bonds, where electrons can freely move, one electron less or more as the structure deviation play no significant role, similarly as electrons and "holes" in semiconductors.

For covalent bond structures, electrons as point charges will tend to bind to many neutral molecules, forming anions. It is similar to "naked" protons.

Near all elements (but noble gases and few exceptions) have positive electron affinity is spite of dense clouds of electrons around their nucleus. It should not be therefore surprising electrons can attach itself to molecules.

An electron can also return to its original place while releasing its energy, or to break a bond and attach to one of fragments.

$$\ce{e- + R3C-H -> R3C- + H^.}$$
$$\ce{e- + R3C-OH -> R3C^. + OH-}$$


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