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other states. In practice, this generally means that a particular wavefunction can be expressed as the sum of two or more other wavefunctions. For example, the wavefunctions for molecules can be formed by the superposition of atomic wavefunctions. A photon wave packet can be formed by the superposition of momentum eigenstates

triple bond—A chemical bond that holds two atoms together by sharing three pairs of electrons. A triple bond is shorter and stronger (harder to pull the atoms apart) than a double or a single bond.

Uncertainty Principle—The statement that the momentum and position of a particle cannot be known exactly simultaneously. If the momentum of a particle is known exactly, then the position is completely uncertain, that is, there can be no information on the position. If the position is known exactly, there can be no information on the magnitude of the momentum. In general, the principle states that the position and momentum can only be known within a certain degree of uncertainty. This is intrinsic to nature and not a consequence of experimental error.

vector—A directed line segment usually represented by an arrow. A vector is a quantity with both magnitude and direction. A car going 60 miles per hour has a speed, which is not a vector. A car going 60 miles per hour north has a velocity, which is a vector because it has a magnitude (60 miles per hour) and a direction (north).

velocity—A vector describing both the speed and the direction in which an object is moving.

wave packet—A superposition of waves that combine to make a particle more or less located in a region of space. The superposition of waves has regions of constructive and destructive interference. The probability of finding the particle is large where there is constructive interference. The superposition of waves more or less localizes a particle in some region of space. The location cannot be perfectly defined because of the Heisenberg Uncertainty Principle.

wavefunction—A solution to the Schrödinger Equation for a particular state of a system, such as an atom or molecule. A wavefunction is a probability amplitude wave. It gives information on finding a particle in a particular region of space. For example, the wavefunctions for the hydrogen atom give the probabilities of finding the electron at different distances and directions from the nucleus.

wavefunction collapse—A state of a system is frequently a superposition of wavefunctions. Each wavefunction has associated with it a definite value of an observable, for example, the energy. Because a superposition is composed of many wavefunctions, it has associated with it many values of an observable. When a measurement is made, the system goes from being in a superposition of wavefunction to being in a single wavefunction with one value of the observable (e.g., the energy). It is said that the measurement causes the wavefunction to collapse from a superposition of states into a single state with one value of the observable. It is not possible to say beforehand which state the superposition will collapse into. Therefore, it is not possible to say ahead of time which value of the observable will be measured.

wavelength—The repeat distance in a wave, that is, the distance from one peak in the wave to another.

Index

absolutely small

absolutely small box

absolutely small object

absolutely small particle

absolutely small quantum particle

absolute size

absolute temperature

absolute zero

absorption

absorption lines

absorption of a photon

absorption of light

absorption spectrum

acetaldehyde

acetate anion

acetic acid

acetobacter

acetylene

Actinides

Actinide series

aether

alcohol dehydrogenase

alcohols

ammonia

angstrom

anion

antibonding molecular orbital (antibonding MO)

arc lamp

aromatic molecules

asymmetric stretch

atherosclerosis

atomic number

atomic orbitals

atom size

Aufbau procedure

Balmer, Johann

Balmer series

band gap

band of states

band of vibrations

band structure