THE PERIODIC TABLE

4.7 - Covalent Bonding

The Hydrogen Molecule

Let's look at the formation of H₂ molecule from the perspective of Lewis Electron-dot symbol of H atoms.

Each H atom has 1 valence electron. When two H atoms react, they share a pair of electrons. In the sharing of a pair of electrons a chemical bond is formed. Because the bond involves sharing of electrons, it is called a covalent bond.
The driving force behind the formation of a H2 molecule is that in the sharing arrangement, each H atom in the H2 molecule is able to achieve a stable arrangement of a filled shell. Put your mouse over and click on the image on the right to have a closer look.

Electrons are not really dots. Let's take a look at another look at this covalent bond in the following representation of electrons.

This is a representation of the electron cloud about the hydrogen atoms. The identical electron clouds about each hydrogen atom indicate that in the hydrogen molecule, the electrons are shared equally between the two hydrogen nuclei because both H atoms have the same electronegativity. The bond that forms between the hydrogen nuclei is said to be a nonpolar covalent bond.(This is to distinguish between polar covalent bonds that will be discussed in section 5.3).

Other diatomic molecules such as

also have nonpolar covalent bonding because the two identical atoms have identical electronegativities.