Question

Why is the term "sodium chloride molecule" incorrect but the term "carbon dioxide molecule" is correct?

Short answer

The term "sodium chloride molecule" is incorrect because sodium chloride (NaCl) is an ionic compound formed by the ionic bond between a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-). It is not a molecule, as it is not formed by covalent bonding. Conversely, the term "carbon dioxide molecule" is correct because carbon dioxide (CO2) is formed by covalent bonding between one carbon atom and two oxygen atoms, creating a neutral particle that meets the definition of a molecule.

Step-by-step solution

Understand the Molecule Definition

A molecule is defined as a neutral particle formed by a group of atoms that are covalently bonded. Covalent bonding involves the sharing of electrons between atoms to achieve stability.

Analyze Carbon Dioxide Formation

Carbon dioxide (CO2) is formed by two oxygen atoms that are covalently bonded to a single carbon atom. In this case, one carbon atom shares its electrons with two oxygen atoms, forming a stable structure. Since CO2 is formed by covalent bonding and consists of a neutral group of atoms, it is appropriate to call it a molecule.

Understand Ionic Compounds Definition

An ionic compound is a compound formed by the electrostatic attraction between oppositely charged ions. It occurs between a metal ion and a non-metal ion, where the metal loses one or more of its electrons to the non-metal, creating a positive ion (cation) that is attracted to the negative ion (anion).

Analyze Sodium Chloride Formation

Sodium chloride (NaCl) is formed by the ionic bond between a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-). The sodium atom loses one electron to the chlorine atom, forming charged ions. The electrostatic attraction between these charged particles forms an ionic lattice structure. Since the formation of sodium chloride involves ionic bonding rather than covalent bonding, it is an ionic compound, not a molecule.

Explain the Correct Terminology

The term "sodium chloride molecule" is incorrect because sodium chloride is an ionic compound, not a molecule formed by covalent bonds. Thus, it is more accurate to call it a "sodium chloride compound" or "sodium chloride crystal." In contrast, "carbon dioxide molecule" is correct because carbon dioxide is formed by covalent bonds between its atoms, creating a neutral particle that meets the definition of a molecule.

Key concepts

Covalent Bonding

Covalent bonding represents one of the fundamental interactions that holds atoms together within a molecule, creating the rich diversity of substances we encounter. In essence, covalent bonds are the outcomes of atoms sharing pairs of electrons to obtain the octet configuration, which is associated with the stability of the noble gases. This sharing creates molecules, such as water (H2O) and methane (CH4), with distinct properties that are critical for life and various chemical processes.

Atoms with similar electronegativity values — a measure of how strongly an atom can attract electrons in a chemical bond — are particularly prone to form covalent bonds. Take the example of carbon dioxide (CO2): a carbon atom forms double bonds with two oxygen atoms, each sharing two pairs of electrons. This type of binding creates a complex interplay of attractions that hold the atoms together but do not result in a net charge, thus forming a neutral molecule. Understanding the principles of covalent bonding is crucial for predicting the behavior and properties of molecules.

Ionic Compounds

Ionic compounds, such as common table salt (sodium chloride or NaCl), stand in contrast to the molecules formed by covalent bonds. These compounds arise from the electrostatic attraction between ions, which are atoms or groups of atoms that have lost or gained electrons to achieve a full outer shell and, consequently, have become charged. In the classic example of sodium chloride, a sodium atom (Na) donates an electron to a chlorine atom (Cl), transforming into a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-).

The resulting electrostatic force of attraction between these oppositely charged ions is the ionic bond, which is non-directional and extends throughout the solid, forming a crystal lattice. Unlike covalently bonded molecules, ionic compounds typically have high melting and boiling points, are often soluble in water, and conduct electricity when molten or dissolved due to the mobility of the ions.

Chemical Terminology

Navigating the language of chemistry is critical for clear communication and understanding. Chemical terminology lays out the nomenclature and classification that help differentiate between various types of substances. For instance, the term 'molecule' is applied specifically to a collection of atoms held together by covalent bonds and usually signifies a neutral entity. On the other hand, the 'formula unit' of an ionic compound refers to the simplest whole-number ratio of ions that represents the compound's composition.

Thus, we describe substances with phrases suited to their binding nature: 'carbon dioxide molecule' is accurate because carbon and oxygen are covalently bonded with no net charge, while 'sodium chloride compound' correctly denotes the ionic lattice structure of NaCl. Grasping these terms not only helps in identifying the nature of the bond and the type of compound but also avoids confusion when communicating chemical concepts.