According to the VSEPR theory, a diatomic molecule will always have a linear shape. This fact is fairly intuitive, as a diatomic molecule will only have two nuclei, and the shortest distance between two points is a straight line. However, differences exist in diatomic molecules based on the number of valence electrons in various diatomic molecules.
VSEPR theory frequently mentions a bond angle to identify the structure. A bond angle is described as the angle between at least two atoms within a molecule. Since a diatomic molecule only contains two molecules in a linear shape, the bond angle is always 180 degrees.
Electronegativity is a term that identifies the tendency of an atom to attract an electron and increase from left to right and from bottom to top on the periodic table. In a linear, diatomic molecule, differences in electronegativity between the two bonded atoms results in a polar molecule and affects its chemical reactivity. In addition, the atom with the highest electronegativity is normally identified as the central atom in diatomic molecular structure.
Most gases in the atmosphere occur as diatomic molecules and include molecular oxygen, nitrogen and hydrogen. Each one of these gases has two molecules of their respective elements and is arranged in a linear shape. Examples of polar diatomic molecules displaying linear molecular geometry include hydrochloric acid and carbon monoxide.