Well i have a conceptual problem with the atomic structure and mass distribution. See we call holes as absence of electrons. So holes are actually nothing but emptiness. As shadow is nothing but the absence of light. However while calculating mass we do include the number of holes too along with the electrons. But why is this. We are once considering the mass of electrons. Why do we need to again consider the mass for the absence of it too??? I tried to find out the reason but none of them could satisfy. Someplaces I even found that they wrote that mass of a hole is even grater than that of an electron. Isn't it a bit fishy??