Surrounding the nucleus of the atom are particles acquiring opposite electric charge from protons. These are termed as electrons. Physicists randomly call the electrons' charge negative, and the protons' charge positive. An electron has the same charge quantity exactly as the proton, but with opposite polarity. The charge on the single electron or proton is smallest which is possible electric charge. All charges, does not matter how large, are multiples of this unit charge.
One of the initial ideas about atom pictured the electrons embedded in the nucleus, like raisins in a cake. Later, the electrons were seen as orbiting nucleus, making the atom like a miniature solar system with the electrons as the planets. Still later, this assumption was modified further. Today, the electrons are seen as so fast- moving, with patterns so complex, which it is not even possible to pinpoint them at any given instant of time. All that can be done is to say that an electron will just as possible be inside a certain sphere as outside. These spheres are called as electron shells. Their centers correspond to position of atomic nucleus. As far the nucleus is from the shell, the more energy the electron posses.
Electrons can move easily from one atom to another in some of the materials. In other substances, it is tough to get electrons to move. But in any case, it is easy to move electrons than it is to move the protons. Electricity almost always results, in some way, from the motion of electrons in a material.
Electrons are much lighter than protons or neutrons. In fact, compared to the nucleus of an atom, the electrons weigh practically nothing.
In general, the number of electrons in an atom is the same as the number of protons. The negative charges therefore exactly cancel out the positive ones, and the atom is electrically neutral. But under some conditions, there can be an excess or shortage of electrons. High levels of radiant energy, extreme heat, or the presence of an electric field can "knock" or "throw" electrons loose from atoms, upsetting the balance.