Atomic and molecular structure

Atomic and molecular structure describes how electrons and nuclei are arranged in atoms and molecules. These arrangements shape chemical bonding, spectra, reactivity, and material properties.

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Atomic orbital: A quantum state of an electron in an atom, described by a wavefunction and characterized by energy and spatial distribution. Orbitals specify the allowed electron distributions that underlie atomic structure.
Schrödinger equation: A fundamental equation describing how the quantum state of a system changes and, in stationary cases, its allowed energies. Its solutions provide the wavefunctions used to calculate electron structure.
Chemical reactivity: The tendency of a substance to undergo chemical change through the breaking and formation of bonds. Electron arrangement and molecular geometry shape which reactions are possible and how fast they proceed.
Lewis structure: A diagram showing molecular connectivity and valence electrons as bonds and lone pairs. It is a compact bookkeeping model, not a full quantum description of electron density.
Electron configuration: The distribution of electrons among an atom’s shells, subshells, and orbitals. Electron configurations summarize how electrons occupy an atom’s available states.
Molecular orbital theory: A model in which electrons occupy orbitals extending over an entire molecule. It explains molecular bonding through electron states distributed across multiple nuclei.
Molecular polarity: The uneven distribution of electrical charge across a molecule, producing a net dipole when the distribution is asymmetric. Molecular structure determines whether bond dipoles cancel or produce an overall dipole.
VSEPR theory: A model that predicts molecular shape by treating electron groups around a central atom as mutually repelling. It predicts many geometries without calculating the underlying electronic wavefunction.
Chemical bond: An interaction that holds atoms together through electrostatic forces and the sharing or transfer of electrons. Bonding converts separate atoms into stable molecular arrangements.
Valence bond theory: A bonding model that describes molecules using localized electron-pair bonds formed from atomic orbitals. It offers a localized-bond picture distinct from molecular orbitals spread across a molecule.