At room temperature, no free electrons can ever leave the surface of the metal. A free electron cannot escape the coulomb (electric) attractive forces presented by the positive metal ions in the lattice. (We'll see later that under special conditions using unique mechanisms, it is possible for electrons to escape)
I don't understand why the electrons can't leave the surface. Even though there is an attractive force from the positive ions there is an almost equal repulsive force from the other free electrons. So the net force should be almost zero, so even a small voltage should be enough to get the free electrons to leave the surface right? What am I missing?
Please keep answers relatively simple. I only have a basic understanding of physics and chemistry.