We analyze the photoelectric effect using photon energy alone. Why isn't the photon momentum a consideration? (It may help to reread the discussion of momentum and energy in connection with pair production.)

When a light source having energy greater than the work function of the metal surface shines on the metal surface, electrons are emitted from the metal surface. This phenomenon is known as the photoelectric effect. The photon interacts with the metal atoms exchanging momentum and energy.

In the photoelectric effect, the photon's kinetic energy is slightly altered as the mass of the interacting atoms is quite large compared to an incoming photon. So, the minute change in kinetic energy of a photon is neglected and energy conservation works perfectly.

Due to the presence of metal atoms, most of the photon's momentum gets transferred to the interacting metal atoms. So, the conservation of total momentum cannot be taken without considering the momentum of the metal atoms.