Chemistry Reference
In-Depth Information
At the same time, scientists are required to make their methods and conclusions
understandable even for nonprofessionals: “Scientists and inventors cannot live
isolated in an ivory tower, they require a sounding board. They need the approval of
those who will benefit from their scientific work in the end.” [
1
]
Many technical terms are used in everyday language, but chemical terms are also
part of it: substance, metal, solution, acid, lye, gas, combustion, are examples. Often
the meaning of such terms in the professional language is different or more
advanced, but it certainly is always more precise then the one in everyday language.
Combustion in our everyday language is an expression for candles or spirits
burning, which afterwards are irretrievable destroyed. At the same time, the expert
thinks about the reaction with oxygen to form the invisible and colorless gases
carbon dioxide and water vapor.
To be able to talk with students about chemical issues in an appropriate way, it is
important to lead them from their everyday language to the chemical terminology
and symbolic language. They should learn to phrase their observations and discuss
explanations in a scientific way.
7.1 Scientific Ideas: Parameters, Units, Terms, Symbols
Much of terminology and nomenclature like parameters and units are historically
grown. For example, 1 mile was defined in ancient Rome as “milia passuums,” i.e.
the distance of 1,000 double steps of a short man (today: 1,475 m). The “statute
mile” in England and the United States was changed to 1,000 double steps of a huge
man (today: 1,609.30 m), and finally in 1875, the unit meter (m) and kilometer (km)
were defined (see the next paragraph).
Those and other units have been redefined a number of times by standard
committees like IUPAC (International Union of Pure and Applied Chemistry) to
achieve more precise and standardized definitions. These problems of nomenclature
and historical changes in the meaning of terms, symbols, parameters, and units are
to be considered in the following.
7.1.1
International System and Derived Units
Three examples of parameters and units shall demonstrate historical changes:
Length.
The meter as a unit of length has been defined in 1875 as the
10,000,000th part of one earth quadrant (1/4 circumference of earth, today's
mean value: 10,000.09 km). It has been set by the length between two marks on a
platinum-iridium bar, located in S
`
vre near Paris since 1889. A more precise
definition of the meter could be obtained with the help of spectroscopic methods:
the meter was redefined in 1960 as equal to 1,650,763.73 wavelengths of the
