Molecular Compounds

Compounds that are composed of only non-metals or semi-metals with non-metals will display covalent bonding and will be classified as molecular compounds. Nitrogen monoxide (NO) will be a covalently bound molecule (two non-metals) and silicon dioxide (SiO₂) will also be a covalently bound molecule (a semi-metal and a non-metal). The basic unit of molecular compounds are called molecules.

Example 1

Provide the classification (i.e. atomic element, molecular element, molecular compound, or ionic compound) of each substance.

1. Fe
2. PCl₃
3. LiBr
4. P₄
5. oxygen gas

SOLUTION

1. Fe, iron is an element that is represented with no subscript, so it is an atomic element.
2. PCl₃ is made up of two nonmetals, so it is a molecular compound.
3. LiBr is made up of lithium, a metal and bromine a nonmetal, so it is an ionic compound.
4. P₄ is a substance that is made up of four atoms of the same element, so it is a molecular element.
5. The formula for oxygen gas is O₂ so it is a molecular element.