Electron Energy Levels


Q1: It is written on our textbook that 'an electron needs an amount of minimum energy called work function in order to escape from a metal surface.' Why should it be a 'minimum' energy? Is it equal to the binding energy of the electron?

Q2: Why is the separation between lines of energy level of atomic hydrogen (in electron volt) decreases from ground state (-13.6eV) upward to energy = zero? Is it because of decreasing nucleus attraction when the electron of hydrogen is being ionized?

Q3: It is writen that 'amount of energy required for excitation of electron can be obtained from "electron bombardment" and "photon bombardment" '. What are "electron bombardment" and "photon bombardment"?


Q1. In a sense it is equal to the binding energy of the electron, but it is the energy binding the electron to the metal as a whole that must be provided. The ionization energy of metals is so low that at room temperatures the outer electrons in metals are free to wander around anywhere in the metal object. This electron soup in which all the atoms share all the electrons is what makes metal so strong, and such a good conductor of electricity.

It is only when I try to remove an electron altogether from the object that I must give it a certain threshold energy called the work function for that metal. You might think of like the escape energy required for a rocket to permanently leave the gravitational field of the Earth. Removing an electron is going to leave a temporary positively charged hole behind. The departing electron must over come the attraction of that hole.

Q2. Actually it is because of the spacing of the quantum energy levels. The electron may only exist at specific energy levels. You would be correct in thinking of the quantum level spacing as dependent on the distance from the nucleus.

Q3. Bombardment refers to a stream of objects, either photons or electrons, being directed at the target atoms. Either electrons or photons can interact with the target atoms to raise them to an excited state.