Final answer:
Resistivity is the key property of wire that depends on its molecular structure and size, determining how well it conducts electricity. Copper is often used due to its low resistivity, high tensile strength, and high ductility, while other materials may offer benefits like reduced weight or cost.
Step-by-step explanation:
The fundamental property of wire that depends on a wire's molecular structure and size is resistivity. Resistivity is an intrinsic property of a material, which is independent of its shape or size and is directly proportional to its resistance. This property is essential for determining how well a wire conducts electricity. Factors such as tensile strength and ductility are also important; for instance, copper is frequently used in wiring due to its low resistivity, high tensile strength, and high ductility. Other materials like aluminum might be used for wiring because they are lighter and less expensive, although they usually have higher resistivity than copper. The physical properties of a material, including conductivity and malleability, depend on the ease with which electrons can be removed, as this affects an element's metallic character.
Moreover, the configuration of atoms and ions, effective nuclear charge, ionization energies, and electron affinities significantly affect a material's chemical reactivity and, by extension, its physical properties. These properties are consequently central to understanding materials' suitability for different applications, such as wiring in electrical circuits.