Chemistry glossary

Clear, contextual definitions linked directly to the simulation where each idea becomes visible.

Atom: The smallest unit of an element that retains its chemical identity, consisting of a nucleus and electrons.
Isotope: Atoms of the same element with the same proton count but different neutron counts.
Ion: An atom or group with net charge because electrons have been lost or gained.
Valence: The electron capacity or bonding behavior associated with an atom’s outer electron arrangement.
Orbital: A quantum state described by a wavefunction, giving the spatial probability distribution for an electron.
Electronegativity: A relative measure of how strongly a bonded atom attracts shared electron density.
Hybridization: An introductory bonding model that combines atomic orbitals into directed hybrid orbitals.
Resonance: A description using multiple contributing Lewis structures when one localized drawing is insufficient.
Oxidation: Loss of electrons or an increase in oxidation number.
Reduction: Gain of electrons or a decrease in oxidation number.
Mole: The amount of substance containing exactly 6.02214076 × 10²³ specified entities.
Chemical equilibrium: A dynamic state in which forward and reverse reaction rates are equal and macroscopic composition is constant.
Entropy: A thermodynamic state function related to energy dispersal and the number of accessible microscopic arrangements.
Enthalpy: A state function H = U + pV whose change equals heat transferred at constant pressure when only pressure-volume work occurs.
Gibbs free energy: The state function G = H − TS; at constant temperature and pressure, its change predicts thermodynamic direction.
Nucleophile: An electron-pair donor that forms a new bond to an electron-poor center.
Electrophile: An electron-pair acceptor that is attacked by an electron-rich species.
Catalyst: A substance that increases reaction rate through a lower-barrier pathway and is regenerated overall.
Activation energy: The energy barrier separating reactants from the transition-state region along a reaction pathway.