Electric Charge
Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charges; positive and negative (commonly carried by protons and electrons respectively). Electric charge is a basic property of electrons, protons and other subatomic particles.
This makes electrons and protons stick together to form atoms. In atoms, the electron carries a negative elementary or unit charge; the proton carries a positive charge. Things that have the same charge push each other away (they repel each other). This is called the Law of Charges. It was discovered by Charles-Augustin de Coulomb. The force of attraction or repulsion between two charged bodies $Q_1$ and $Q_2$ can be determined by Coulomb's law:
Mathematically, this is given as:
$$F= {{kQ_1 Q_2} \over {r^2}} (newtons, N) . . . . . Eq. (1)$$
where $F$ is in newtons, $k$ = a constant = $9.0 \times 10^{-9} Nm^{2}/C^{2}$, $Q_1$ and $Q_2$
are the charges in coulombs ($C$), and $r$ is the distance in meters between the two charges. In particular, note the
squared $r$ term in the denominator, resulting in rapidly decreasing levels
of $F$ for increasing values of $r$.
In the atom, therefore, electrons will repel each other, and protons
and electrons will attract each other. Since the nucleus consists of many
positive charges (protons), a strong attractive force exists for the electrons
in orbits close to the nucleus [note the effects of a large charge $Q$
and a small distance $r$ in Eq. (1)]. As the distance between the nucleus
and the orbital electrons increases, the binding force diminishes until it
reaches its lowest level at the outermost subshell (largest $r$). Due to the
weaker binding forces, less energy must be expended to remove an
electron from an outer subshell than from an inner subshell. Also, it is
generally true that electrons are more readily removed from atoms having
outer subshells that are incomplete and, in addition, possess few
electrons. These properties of the atom that permit the removal of electrons
under certain conditions are essential if motion of charge is to be
created.