A physics textbook I am currently reading states that
"if an electron with kinetic energy equal to 1.12 aJ collides with a single mercury atom in its ground state, the atom may be excited and the electron will lose kinetic energy. If the same atom is hit by a photon with an energy of 1.12 aJ, the photon will not be absorbed, and the atom will not be excited by the photon."
I am a bit confused about this. Why is it that the electron may excite the atom, but the photon may not, when they both carry exactly the same amount of energy?
if anyone can explain the statement to me, then I would greatly appreciate it!