AtomsinMolecules

Atoms in molecules are the constituent atoms that are joined by chemical bonds to form a discrete unit called a molecule. Molecules may consist of one element (O2, N2) or multiple elements (H2O, CO2). Bonding results from atoms seeking stable electron configurations; the most common interaction in organic and many inorganic substances is covalent bonding, in which atoms share electron pairs. Other types include ionic bonds, where electrons are transferred, creating charged species that attract; metallic bonds in metals; and hydrogen bonding as an important intermolecular interaction.

Within a molecule, atoms arrange in characteristic geometries around central atoms, described by theories such as VSEPR, which relates electron-pair repulsion to bond angles. Bond lengths and angles depend on bond order, atom sizes, and electronegativity. The overall shape of a molecule influences physical properties and reactivity, including polarity determined by the distribution of electronegative atoms.

Molecular formulas express composition (empirical and molecular formulas, e.g., H2O, CH4). Structural representations include Lewis diagrams and ball-and-stick or space-filling models. Molecules can have isomers: same atoms, different connectivity (structural) or different spatial arrangement (stereoisomers).

At the level of theory, valence bond and molecular orbital descriptions explain bonding and bonding patterns, including sigma and pi bonds. Molecules are dynamic systems, with vibrational and rotational motions that affect spectra and reactivity.

Understanding atoms in molecules underpins chemistry, biochemistry, and material science, linking composition and structure to properties and behavior.