Question

Classify each of the following species as molecular, network covalent, ionic, or metallic. (a) Na (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (d) \(\mathrm{C}_{60}\) (e) \(\mathrm{HCl}(a q)\)

Short answer

Question: Classify the following species into one of four categories: molecular, network covalent, ionic, or metallic. (a) Na (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (Sodium Sulfate) (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (Benzene) (d) \(\mathrm{C}_{60}\) (Buckminsterfullerene) (e) \(\mathrm{HCl}(a q)\) (Hydrochloric Acid in water) Answer: (a) Na - Metallic (b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) - Ionic (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) - Molecular (d) \(\mathrm{C}_{60}\) - Network Covalent (e) \(\mathrm{HCl}(a q)\) - Ionic

Step-by-step solution

(a) Na

Sodium (Na) is an element in the alkali metal group. The bonding between alkali metal atoms is characterized by metallic bonds, in which valence electrons are free to move throughout the positively charged metal lattice. Therefore, Na is a metallic species.

(b) \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) (Sodium Sulfate)

Sodium sulfate, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\), is an ionic compound composed of positively charged sodium ions (\(\mathrm{Na}^{+}\)) and negatively charged sulfate ions (\(\mathrm{SO}_{4}^{2-}\)). The attraction between these positive and negative ions creates an ionic bond. Therefore, \(\mathrm{Na}_{2} \mathrm{SO}_{4}\) is classified as an ionic species.

(c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (Benzene)

Benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\), is an organic compound with alternating single and double bonds between carbon atoms, and hydrogen atoms attached to the carbon atoms. The bonding within the molecule is covalent, and there is no extended network or much intermolecular attractions that would make it network covalent. Therefore, benzene is classified as a molecular species.

(d) \(\mathrm{C}_{60}\) (Buckminsterfullerene)

Buckminsterfullerene, \(\mathrm{C}_{60}\), is a form of pure carbon in which the carbon atoms are arranged in a series of interconnected hexagons and pentagons, forming a hollow sphere-like structure. Each carbon atom is covalently bonded to three other carbon atoms; however, the resulting substance forms a stable network of covalent bonds, known as a network covalent substance. Therefore, \(\mathrm{C}_{60}\) is classified as a network covalent species.

(e) \(\mathrm{HCl}(a q)\) (Hydrochloric Acid in water)

When hydrogen chloride (HCl) dissolves in water, it forms an aqueous solution of hydrochloric acid, denoted as \(\mathrm{HCl}(a q)\). In this case, the hydrogen and chlorine atoms within HCl are held together by a covalent bond in the gas phase; however, when dissolved in water, they dissociate into positively charged hydrogen ions (\(\mathrm{H}^{+}\)) and negatively charged chloride ions (\(\mathrm{Cl}^{-}\)), forming an ionic species in solution. Therefore, \(\mathrm{HCl}(a q)\) is classified as an ionic species.

Key concepts

Metallic Bonding

Understanding metallic bonding is crucial for deciphering the properties of elements like sodium (Na). Metallic bonds are formed when atoms share a 'sea' of delocalized electrons. This electron cloud surrounds the positively charged atomic nuclei of metal atoms.

Imagine these electrons as birds flying freely between trees in a forest; the trees are the metal cations, and the forest is the metallic structure. This type of bonding is responsible for the characteristic properties of metals such as conductivity, malleability, and ductility. In sodium's case, its metallic bonding gives it a lustrous appearance and the ability to conduct electricity, categorizing it as a metallic species.

Ionic Compounds

Ionic compounds, like sodium sulfate (Na₂SO₄), are made up of positive and negative ions that attract each other.

The principle is similar to how magnets work: positive ions (cations) and negative ions (anions) are drawn together to form a crystal lattice. Ionic compounds have high melting and boiling points and they dissolve in water to form electrolyte solutions. These properties of sodium sulfate confirm its structure as an ionic species, based on the strong attractions holding its ions together.

Molecular Species

Molecular species, such as benzene (C₆H₆), consist of a set number of atoms bonded covalently.

This species is akin to a group of friends holding hands; they are connected but separate from other groups. The molecular species exhibit distinct molecules with unique chemical and physical properties dependent on their atomic arrangement and molecular shape. Benzene, for example, has a planar hexagonal ring structure giving it particular stability and leading to its classification as a molecular species.

Network Covalent Substances

One example of network covalent substances is Buckminsterfullerene (C₆₀). These substances have atoms connected by covalent bonds in a continuous network that extends throughout the material.

Visualize it as a construction set where each piece is bonded to several others to create a vast, interlinked structure. This arrangement leads to very high melting points and hardness. The intricate spherical shape of C₆₀ illustrates this perfectly, as the carbon atoms form a strong, stable matrix.

Chemical Species Classification

The classification of chemical species into categories such as molecular, network covalent, ionic, or metallic is fundamental to understanding their properties and behavior.

Each classification corresponds to a specific type of atomic interaction and structure, influencing the substance's physical characteristics. The dissociation of hydrogen chloride in water to form an ionic solution demonstrates how the classification can change depending on the environment, emphasizing the importance of context in chemical species classification.