If electrons come near a positive charge, the two fields reached out and attract each other evens though there may be some distance between them. it is the attraction between the positive charge and nucleus of the electrons in the outer orbits that determine the electrical characteristic of a material.  if an atom of a particular material is so constructed that there is a very small attraction between the positive materials and outer electrons, the outer electrons are free to leave the atom when they are under the influence of an electric field.  

Such a condition exists in metal, silver, copper, and aluminum have a very weak attractive force between the nucleus and the outer electrons. substance glass, plastic, wood, and baked clay have a powerful bond between the nucleus and the outer electrons, and these electrons will not leave their atoms unless very strong electric fields are applied.

You learn that a dry cell has a particular property of having an excess of electrons at its positive terminals. suppose you examine just what happened when a metal wire is connected across the terminals of a dry cell.

The amount the wire is connected across the cell there will be an excess of electrons at the negative end and the shortage on a positive end. remember that electrons repel each other and are attracted to the place where there is a shortage of electrons now have a place to go. the field of these electrons pushes again the electrons in the atoms of the wire. and some of these outer electrons are pushed out of their atoms.

These free electrons cannot remain where they are since their electric field force there away from the piled up electrons at the negative terminals, so they are forced away from the negative terminals when these newly freed electrons arrive at the next atom, they in of force these outers electrons off their atoms and the process continues.

At the positive end of the wire there is a shortage of electrons, and their force there is a strong attraction between the positive terminals and the outer electrons of nearby atoms. these electric fields of the outer electrons are shortly pulled by the electric field of positive terminals and some of the electrons leave their atoms and move toward a positive end.when these elecctrons leave their atoms , the atom becomes positively charged and electron from the next atom are attracted toward the positive end , and the process continuous.