Why is the term “sodium chloride molecule” incorrect whereas the term “carbon dioxide molecule” is correct?

A molecule is defined as the smallest particle in a chemical substance that has the chemical properties of that substance. It is formed when two or more atoms combine together through covalent bonds, which involve the sharing of electrons between atoms. Molecules are typically associated with covalent compounds.

Sodium chloride (NaCl) is an ionic compound, which means it is formed by the transfer of electrons between atoms, resulting in the formation of ions with opposite charges. In the case of sodium chloride, a sodium atom (Na) loses one electron to become a positive ion (Na+), while a chlorine atom (Cl) gains one electron to become a negative ion (Cl-). These ions are attracted to each other due to their opposite charges, forming an ionic bond. On the other hand, carbon dioxide (CO2) consists of one carbon atom (C) and two oxygen atoms (O). The carbon and oxygen atoms form covalent bonds, with each oxygen atom sharing two electrons with the carbon atom, resulting in a double bond between the carbon and oxygen atoms.

Since a molecule is formed by atoms sharing electrons through covalent bonds, the term "sodium chloride molecule" is incorrect because sodium chloride is an ionic compound and not a covalent compound. In fact, sodium chloride forms a crystal lattice structure where each sodium ion (Na+) is surrounded by six chloride ions (Cl-), and each chloride ion is surrounded by six sodium ions. This continuous arrangement of ions does not form distinct molecules. Instead, sodium chloride exists as a three-dimensional network of ions in a lattice structure.

The term "carbon dioxide molecule" is correct because carbon dioxide is a covalent compound, which means that it is formed by the sharing of electrons between atoms. In a carbon dioxide molecule, one carbon atom is covalently bonded to two oxygen atoms through double bonds. As such, it meets the definition of a molecule as the smallest particle in a chemical substance that has the chemical properties of that substance.