Learning Outcomes:

After this lesson, you should be able to:

• Compare and contrast ionic and covalent bonds.

Electrons are small particles with almost no mass and carry a negative charge. They orbit around the nucleus of an atom similar to how the moon orbits around the earth. The outermost electrons of an atom determine the chemical behavior of atoms. When electrons are transferred or shared between atoms, chemical bonding occurs. There are two types of these bonds, ionic and covalent.

Ionic Bonds

Atoms are electrically neutral because the number of protons equals the number of electrons in naturally occurring atoms. Atoms can donate or receive electrons from other atoms. When this occurs, the number of protons and neutrons are no longer equal, and the result is a charged particle called an ion. After an atom loses an electron, it now has a positive (+) charge because the number of protons is greater than the number of electrons. Vice versa, when an atom gains an electron, the atoms has a negative (-) charge, because the number of electrons is greater than the number of protons. A positively charged ion is called a cation. A negatively charged ion is called an anion. Opposing charge are attracted to each other and as a result stay close together, forming an ionic bond.

Covalent Bonds

A covalent bond is the result of atoms sharing electrons. The resulting combinations of atoms bonding together is called a molecule. The sharing of one pair of electrons by two atoms results in a single covalent bond. A double covalent bond results when two atoms share 4 electrons, 2 from each atom.

When electrons are shared equally between atoms, the bonds are called non-polar covalent bonds. However, atoms bound to one another by a covalent bond do not always share their electrons equally because the nucleus of one atom attracts the electrons more strongly then does the nucleus of the other atoms. Bonds of this type are called polar covalent bonds and are common in both living and nonliving matter. Polar covalent bonds can result in polar molecules, which have a difference in charge (+/-).