molécules

A molecule is the smallest unit of a chemical substance that retains the properties of that substance. It is composed of two or more atoms held together by covalent bonds, forming a discrete unit with a defined arrangement. Molecules can be elements, such as diatomic O2 or N2, or compounds, such as H2O or CO2, made from two or more different elements.

Structure and representation: The molecular formula gives the types and numbers of atoms present, while a structural formula or three-dimensional model shows how the atoms are connected and arranged in space. Molecular geometry, influenced by electron pair repulsion, affects polarity and reactivity.

Bonding and properties: Covalent bonds result from sharing electron pairs. Molecules may be nonpolar or polar, influencing solubility and interactions with other molecules. Intermolecular forces, such as van der Waals forces and hydrogen bonds, govern phase behavior, boiling and melting points, and biological interactions.

Size and diversity: Molecules range from simple diatomic species to large macromolecules like proteins and nucleic acids. Polymers are long chains formed by repeating units. The study of molecules encompasses their synthesis, transformation, and function in chemistry, biology, and materials science.

Measurement and analysis: Properties are quantified by molecular formulas, molar mass (in g/mol), and structural data obtained through spectroscopy, crystallography, and computational chemistry. Understanding molecules provides a framework for predicting chemical behavior and designing substances for specific applications.