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U, V, W, Y


   
Unimolecular Occurring to or within a single molecule; like intramolecular, but can refer to fragmentation reactions.
   
Unsaturated Possessing double or triple bonds.
   
Valence electrons Electrons that can participate in bonds and in chemical reactions; lone-pair electrons are valence electrons, although not participating in a bond.
   
Valence In covalent compounds, the valence of an atom is the number of bonds it forms to other atoms.
   
Van der Waals force Any of several intermolecular attractive forces not resulting from ionic charges; in this volume, only London dispersion forces are described by this name. Descriptions of the potential energy of nonbonded interactions follow the convention of expressing van der Waals attractive forces and overlap repulsion forces as a single van der Waals potential.
   
Wave function In quantum mechanics, a complex function extending over the configuration space of a system; its complex conjugate yields the probability density function, and other mathematical operations yield other physical quantities.
   
Work Energy transferred by applying a force over a distance; lifting a mass does work against gravity, and stores gravitational potential energy.
   
Young's modulus A modulus relating tensile (or compressive) stress to strain in a rod that is free to contract or expand transversely in accord with its Poisson's ratio. The relevant measure of strain is the elongation divided by the initial length.

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