Word of the Week

Curious about those terms in physical chemistry? Here are some etymologies...

• eigenvalue A translation of a German term. The prefix "eigen" is best translated for quantum mechanics as "characteristic". Chemists often use the eigenvalues to "characterize" or "classify" the wavefunctions or states of a systems. For example, the 1s orbital takes its designation from two eigenvalues of the wavefunction: n=1 and l=0. "Among those..trying to acquire a general acquaintance with Schrödinger's wave mechanics there must be many who find their mathematical equipment insufficient to follow his first great problem to determine the eigenvalues and eigenfunctions for the hydrogen atom. " Nature 23 July 1927
• bra A term coined by Dirac in 1947 to describe a vector in a function space that represents a wavefunction's complex conjugate. Kets are the notation for the corresponding vector representing a wavefunction. The words come from splitting "bracket", since when combined, the notation for looks like a bracket. "We shall call the new vectors bra vectors, or simply bras, and denote a general one of them by the symbol < |, the mirror image of the symbol for a ket vector." P. A. M. DIRAC in Principles of Quantum Mechanics
• quantophrenic A term used for an obsession with and exaggerated reliance upon mathematical methods or results. (Source Oxford English Dictionary). For a long time, chemists considered quantum theorists to be quantophrenics. The following quote summed it up well: "Every attempt to employ mathematical methods in the study of chemical questions must be considered profoundly irrational and contrary to the spirit of chemistry. If mathematical analysis should ever hold a prominent place in chemistry - an aberration which is happily almost impossible - it would occasion a rapid and widespread degeneration of that science." Auguste Comte, Cours de Philosophie Positive, 1830. Fortunately, quantum chemists persisted, and the methods they developed to treat chemical systems have become powerful tools for chemists in many areas.
• catalyst Coined by Berzelius (in Edin. New Phil. Jrnl. XXI. 223 Many bodies..have the property of exerting on other bodies an action which is very different from chemical affinity. By means of this action they produce decomposition in bodies, and form new compounds into the composition of which they do not enter. This new power, hitherto unknown, is common both in organic and inorganic nature..I shall..call it catalytic power. I shall also call Catalysis the decomposition of bodies by this force. ) Comes from the Greek for dissolution. (Source Oxford English Dictionary)
• effusion comes from the French, to pour out, or to shed blood.
• fugacity comes from the Latin "fugare", to flee. The same root gives us fugitive.