Generally, metals on the Periodic Table of the Elements have a positive charge (a positive ion) and the nonmetals have a negative charge (a negative ion). There are several exceptions to this rule. A chemical reaction can take place when a positively charged element meets a negatively charged element.   This can create an overall charge of zero, making a compound that is electrically neutral and stable.

There are various types of chemical bond and the way that these bonds are arranged is unique to that substance.  We will be concerned with two types of bonds:  ionic and covalent. When energy differences between atomic orbitals of two atoms are large, there is a sharing of electrons which we call ionic.  Ionic bonds are formed when electrical charges (positive and negative) come together to form neutral substances.  The best example of a substance with an ionic bond is table salt.  Salt consists of sodium ions (+) and chlorine ions (-).  When these + and - ions come together they form salt, a stable substance.  Notice that sodium is considered a “metal” and chlorine is considered a “non metal.”  Compounds that are created through ionic bonding are referred to as ionic compounds or a transfer of electrons from metal to non metal.

Covalent compounds are usually atoms of nonmetals bonded by shared electron pairs.  When electrons in the outer orbitals combine, they form a different shaped orbital.  Presently we do not understand all the movements, but they are more tightly combined than ionic bonds. Some elements like helium (He), have complete full energy shells and rarely bond with other atoms.  This is typical of the Noble Gases  (Group 18).