Although atoms with equal numbers of protons and electrons exhibit no electrical charge, it is common for atoms to attain the stable electronic configuration of the inert gases by either gaining or losing electrons. The metallic elements on the left side of the periodic table have electrons in excess of the stable configuration. Table
1 shows the electron loss necessary for three light metals to reach a stable electron structure.
The positive charge on the resulting metal ion is due to the atom possessing more nuclear protons than orbital electrons. The valence electrons are most distant from the nucleus; thus, they are weakly held by the electrostatic attraction of the protons and, consequently, are easily stripped from atoms of the metals.
By contrast, the nonmetallic elements on the right side of the periodic table have fewer electrons than that of a stable configuration and can most readily attain the stable configuration of the inert gases by gaining electrons. The negative charge on the resulting nonmetal ion is due to the atom possessing more orbital electrons than nuclear protons. Table 2 compares three nonmetals to the inert gas argon.
Because metallic elements tend to lose electrons and nonmetallic elements tend to gain electrons, a pair of contrasting elements will exchange electrons so that both achieve stable electronic configurations. The resulting ions of opposite charge have a strong force of electrostatic attraction, which is called an ionic bond. Note: This bond forms through the complete transfer of electrons from one atom to another, in contrast to the electron sharing of the covalent bond.
The force of attraction between two points of opposite electrical charge is given by Coulomb's law:
where q + is the positive charge, q – is the negative charge, and d is the distance between the two charges. This law of electrostatic attraction can be used to measure the distance between two spherical ions because the charges can be considered to be located at the center of each sphere. (See Figure 1.)
Figure 1. The distance between ionic charges.