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Chemistry classify


									A Chemistry Categorization Shift
How affinity among elements came to be seen as atomic bonding based on mechanical and mathematical laws

Affinity Theory
• Dates to before the early Greeks • Personified the elements with allegories of love and hate relationships. • Elements have affinities or attractions to some other elements and, revulsions or hostilities to others.

An Example of Affinity
• Alcohol has a greater greater affinity for water than for salt.
– If you add alcohol to salt water, the liquids will mix... – …And the salt will precipitate out as a solid. – So the alcohol drove the salt away.

• Caveat: alcohol and water have mixed, but not combined chemically.

Geoffroy’s 1718 Table of Affinities Uses Symbols from Alchemy

The Shift to Mechanical Theory
• John Dalton (1766-1844) considers the physical components of elements, not their human-like “personalities.” • Different types of atoms with different atomic weights. • Atoms combine according to laws of proportions.
– 8 parts by weight of oxygen combine with 6 parts weight of carbon to form carbon monoxide.

Dalton’s Mechanical Atoms in an 1808-10 Book

The Karlsruhe Congress: 1860
• Chemists convened to try to standardize nomenclature and symbolism • Organized by Carl Weltzien and F. A. Kekule • Problem of terms such as atom, molecule, equivalent, atomic • Established precedence for international discussions among chemists

Conclusions • The paradigm shift in chemistry depersonalized the elements and ended the ideas of alchemy. • The technical symbols used to depict reality illustrate our view of how it works. Shift from symbols as pictures of chemical with personalities to symbols of chemicals as mechanisms with parts. • Are there shifts in symbols in engineering?

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