What is a molecule defined by?

A molecule is defined as a group of two or more atoms that are chemically bonded together, representing the smallest fundamental unit of a chemical compound. These atoms can be of the same element, forming diatomic molecules like O₂, or of different elements, forming compounds like H₂O. Molecules can vary in size and complexity, from simple diatomic molecules to large macromolecules such as proteins and DNA. The specific arrangement and types of atoms within a molecule determine its chemical properties and behavior.