Question

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

Short answer

The term "sodium chloride molecule" is incorrect because sodium chloride is an ionic compound, not a covalent compound. It forms a crystal lattice structure of ions rather than distinct molecules. On the other hand, "carbon dioxide molecule" is correct because carbon dioxide is a covalent compound, with one carbon atom covalently bonded to two oxygen atoms through double bonds. It meets the definition of a molecule as the smallest particle in a chemical substance that has the chemical properties of that substance.

Step-by-step solution

Understanding the Term "Molecule"

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.

Identifying the Type of Bonds in Sodium Chloride and Carbon Dioxide

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.

Explaining Why "Sodium Chloride Molecule" is Incorrect

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.

Explaining Why "Carbon Dioxide Molecule" is Correct

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.

Key concepts

Ionic Compounds

Ionic compounds are fascinating structures formed by the transfer of electrons between atoms. This transfer leads to the formation of charged particles known as ions.
These ions possess opposite charges, which result in the creation of strong ionic bonds due to electrostatic attraction. For instance, sodium chloride (NaCl) is a classic example of an ionic compound.
Here, sodium donates an electron to chlorine. This transaction creates a positively charged sodium ion (Na+) and a negatively charged chloride ion (Cl-).

• These ions arrange themselves in a repeating geometric pattern to minimize potential energy and maximize attraction among opposite charges.
• The result is a rigid and stable three-dimensional lattice structure.

Ultimately, ionic compounds generally have high melting and boiling points as the forces of attraction between ions require substantial energy to break.
They also tend to dissolve in water and other polar solvents, conducting electrical current as ions become free to move.

Covalent Bonds

Covalent bonds are a crucial aspect of molecular substances. Unlike ionic bonds, covalent bonds form when two atoms share one or more pairs of electrons.
This bond occurs because atoms strive to achieve a full outer electron shell, adhering to the octet rule.
Commonly found in nonmetals, covalent bonds vary in strength depending on the number of shared electron pairs and the participating elements.

• A single covalent bond occurs when one pair of electrons is shared between two atoms.
• A double bond involves the sharing of two pairs, and a triple bond three pairs.

Covalent bonds form discrete molecules with distinct characteristics. An excellent example of a covalent bond is found in carbon dioxide (CO2).
In CO2, the carbon atom forms two double bonds with two oxygen atoms. This sharing of electrons defines the molecule's properties and behaviors.

Chemical Bonding

Chemical bonding is the force that holds atoms together in chemical substances. Essentially, there are three primary types of chemical bonds: ionic, covalent, and metallic.
Each type of bond involves a unique mechanism of attraction between participating atoms.

• Ionic bonding: Involves the complete transfer of electrons from one atom to another, leading to the formation of ions.
• Covalent bonding: Entails the sharing of electrons between atoms, primarily seen in nonmetals.
• Metallic bonding: Seen in metals, involves a 'sea of electrons' that are free to move around.