A Level Chemistry OCR Practice Exam

A molecule is defined as a group of atoms that are bonded together, specifically through covalent bonds. Covalent bonds form when atoms share electrons in order to achieve a more stable electron configuration. This distinct interpersonal relationship between atoms results in the formation of discrete units, which we refer to as molecules.

The importance of covalent bonding in defining a molecule highlights why the correct choice is centered on this type of bonding. Molecules can vary in size and complexity, ranging from simple diatomic molecules like O₂ to larger organic compounds, but they all maintain the characteristic of being held together by covalent interactions.

The other choices do not accurately represent the definition of a molecule. A single atom of an element does not form a molecule unless it combines with other atoms; ionic bonds typically create ionic compounds rather than covalent molecules; and a large structure composed of multiple compounds may refer to a mixture or a complex material like a crystal lattice, which does not fit the definition of a single molecule.