How are Covalent Bonds Formed

The idea of chemical bonding was first suggested in 1916 by W. Kossel and G.N. Lewis. They found that all the noble gasses maintain eight electrons in their outer shells with the exception of helium, where only two electrons are present in the outer shell. They also proposed that all other elements try to achieve the configuration of noble gasses by losing, gaining or sharing electrons when they form compounds. This was the basis for early concepts on how chemical bonds are formed.

This article looks at,

     1. What are Different Types of Chemical Bonds
          – Ionic Bond
          – Covalent Bond
          – Metallic Bond

2. How are Covalent Bonds Formed

What are Different Types of Chemical Bonds

There are three main types of chemical bonds: ionic, covalent, metallic. The bond type depends on the electron number and the arrangement of electrons in orbits of atoms. In addition, there is a different type of bond called intermolecular bonds, which includes hydrogen bonds, dipole bonds, and dispersion bonds.

Ionic bonds occur when metal atoms give electrons to non-metal atoms. Thus, ionic bonds occur between metals and non-metals (ex: Sodium chloride).

Covalent bonds occur through sharing of valence electron between two atoms.

Metallic bonds are quite similar to covalent bonds as they share electrons among atoms. But unlike covalent bonds, the valence electrons that hold the atoms together move freely within the metal lattice.

Now, let’s see how are covalent bonds formed.

A covalent bond occurs when two non-metal atoms share their electrons to achieve the noble gas electron configuration. Instead of giving or receiving electrons, each atom will share electrons by overlapping their outer most orbit. These shared electrons are called valence electrons. The simultaneous forces between two positively charged nuclei towards shared electrons keep both atoms together. Single, double and triple bonds are seen only in the covalent compounds. A single covalent bond occurs when a single electron pair is involved. In this case, each atom shares a single electron. A double bond occurs when two pairs of electrons are involved. In this case, each atom provides two electrons for the bond. When forming a triple bond, three pairs of electrons are involved. In triple bonds, each atom shares three electrons in their outer shell. The molecules formed by covalent bonds are called covalent molecules.

Covalent compounds possess many similar properties since they share electrons. All covalent solids can be categorized into two categories: crystalline solids and amorphous solids. Crystalline solids are hard materials. Diamond is an example of a crystalline solid and it is the hardest material on earth. Amorphous solids are not very hard solids. In covalent substances, electricity cannot be conducted due to lack of free-electrons. Thus, covalent compounds are known to be good insulators. Some common examples of covalent compounds include hydrogen gas, oxygen gas, carbon dioxide gas, methane, silicon dioxide, diamonds, etc.

Reference:

Burton, George. Chemical Ideas – Salters advanced chemistry. Vol. 4. N.p.: Heinemann, 2000. Print.

West, Krista. The Basics of Chemical Reactions. N.p.: The Rosen Publishing Group, 2013. Print.

Myers, Richard. The Basics of Chemistry. N.p.: Greenwood Publishing Group, 2003. Print.

Image Courtesy:

“Covalent Bonds” By BruceBlaus – Own work (CC BY-SA 4.0) via Commons Wikimedia