Question

What is the fundamental difference between a molecular substance and a nonmolecular substance?

Short answer

The fundamental difference between molecular and nonmolecular substances is the way their constituent particles are arranged and bonded. Molecular substances are made up of molecules comprising atoms covalently bonded together, while nonmolecular substances consist of atoms or ions (not bonded into molecules) that are arranged in a lattice structure and held together by either ionic or metallic bonds.

Step-by-step solution

Molecular Substances

Molecular substances consist of molecules which are groups of atoms bonded together. These substances have covalent bonds, which involve the sharing of electrons between their constituent atoms. Examples of molecular substances are water (H2O), carbon dioxide (CO2), and methane (CH4).

Nonmolecular Substances

Nonmolecular substances, on the other hand, consist of either atoms or ions that are not bonded together into molecules. There are two main types of nonmolecular substances: ionic compounds and metallic substances. Ionic compounds consist of positively and negatively charged ions arranged in a crystal lattice structure, held together by electrostatic forces or ionic bonds. Examples of ionic compounds include sodium chloride (NaCl), potassium iodide (KI), and calcium carbonate (CaCO3). Metallic substances consist of a lattice of metal ions surrounded by a sea of delocalized electrons and held together by metallic bonds. Examples include copper, iron, and gold.

Fundamental Difference

The fundamental difference between molecular and nonmolecular substances is the way their constituent particles are arranged and bonded. Molecular substances are made up of molecules comprising atoms covalently bonded together, while nonmolecular substances consist of atoms or ions (not bonded into molecules) that are arranged in a lattice structure and held together by either ionic or metallic bonds.

Key concepts

Covalent Bonds

Imagine a group of friends sharing toys equally. This is how covalent bonds work at the atomic level. Atoms come together and share electrons to obtain stability, much like the completion of a puzzle.

Covalent bonds form when two nonmetal atoms have similar electronegativity and hence similar attractions for their bonding electrons. This results in the electrons being shared rather evenly between the atoms. A classic example would be hydrogen (H) atoms bonding with each other to form H2 gas. Each hydrogen atom shares its single electron, creating a strong connection that binds them together. Water (H2O) is another example where oxygen shares electrons with two hydrogen atoms.

Ionic Compounds

In contrast to the equal sharing in covalent bonds, imagine a more dominating friend who takes a toy from another, resulting in one happy and one sad friend. In the atomic world, this is what happens in ionic compounds—atoms with differing electronegativity transfer electrons.

The atom that loses an electron becomes a positively charged ion, while the atom that gains an electron becomes a negatively charged ion. These opposite charges attract each other, leading to the formation of an ionic bond. Table salt (NaCl) is the poster child of ionic compounds, with sodium (Na) giving up an electron to chlorine (Cl), creating a lattice structure of alternating charges.

Metallic Bonds

Metallic bonds can be likened to a community sharing a common garden. In metals, a 'sea' of free-flowing electrons surrounds a regular array of positively charged metal ions.

These delocalized electrons enable metals to conduct electricity and heat and also give them their malleability and ductility. Rather than a bond between specific atoms, it’s a collective bond that holds the structure together. This communal bond allows metals to bend and be shaped without breaking, unlike ionic or covalent compounds which can be brittle. Copper, a metal used in electrical wiring, is a prime illustration of a substance with metallic bonds.

Chemical Structure

The chemical structure of a substance is like its architectural blueprint. It dictates everything from its physical properties to its reactivity.

Molecular substances have a definitive chemical structure where molecules are arranged in a specific geometric layout. Nonmolecular substances do not have discrete molecules but exist as extended structures—a network of ions or metal atoms. Chemical structure is key in understanding a substance's phase at room temperature, its solubility in water, and its melting point among other characteristics. For example, diamond has a rigid network of covalently bonded carbon atoms, making it extremely hard.

Electron Sharing

Electron sharing is at the heart of molecule formation. It's like a potluck where everyone brings something to the table, and all enjoy a greater feast.

Atoms share electrons to fill their outer shells and attain a stable, lower energy state similar to that of noble gases. The number of shared electrons depends on how many electrons are needed to complete an atom’s outer shell. For instance, nitrogen atoms need three more electrons to fill their outer shell, hence two nitrogen atoms share three electrons each to form the stable N2 molecule. It's this sharing that defines covalent bonding and distinguishes it from ionic interactions where electrons are transferred, not shared.