Classification essays rank the groups of objects according to a common standard. For example, popular inventions may be classified according to their significance to the humankind.
Classification is a convenient method of arranging data and simplifying complex notions.
When you select a topic, do not forget about the length of your paper. Choose the topic you will be able to cover in your essay, do not write about something global or general.
Consider these examples:
- Evaluate the best to worst methods of upbringing.
- Rate the films according to their influence on people.
- Classify careers according to the opportunities they offer.
You should point out the common classifying principle for the group you are writing about. It will become the thesis of your essay.
It is important for you to use clear method of classification in your essay, especially when you are dealing with subjective categories such as "quality" or "benefit". Make sure you explain what you mean by this term.
To organize a classification essay, the writer should:
- categorize each group.
- describe or define each category. List down the general characteristics and discuss them.
- provide enough illustrative examples. An example should be a typical representative of the group.
- point out similarities or differences of each category, using comparison-contrast techniques.
Elements and Atoms: Classification of ElementsThe following group of selections returns to the elements, taking up their classification in the 1860s. When this work last looked at the elements (end of the first section) toward the end of the 18th century, we saw the elements of the ancients finally fading from chemistry. In the meantime, dozens of elements were either discovered or first isolated. Each discovery provided a new material to be characterized physically and chemically: how dense is it? at what temperature does it melt? with what other elements does it react, and in what proportions? The number of elements known by the middle of the 19th century led chemists to group them according to similarities and differences in their properties.
Among the properties measured for each new element was the atomic weight or, for those investigators agnostic with respect to atoms, the equivalent weight. In the 50 years after Dalton's atomic hypothesis, the determination of atomic weights suffered from uncertainties in chemical formulas. The development of new tools for chemical analysis and more accurate techniques could determine with ever more precision the composition of compounds in terms of mass ratios. But what those masses represented remained unclear. For example, magnesium oxide was 60% magnesium and 40% oxygen by weight; but how many atoms of each element do those ratios represent?
More than 100 of Europe's most prominent chemists gathered in Karlsruhe in 1860 to try to reach some agreement about atomic weights, nomenclature, and even such fundamental terms as atom, molecule, equivalent. [Wurtz] The Congress adjourned without reaching any definite agreements. Yet the views of Stanislao Cannizzaro, disseminated to congress participants in a pamphlet, won near universal acceptance within a very few years. The pamphlet [Cannizzaro 1858] adopted Avogadro's hypothesis [Avogadro 1811]; it removed the objections the hypothesis had originally faced, and sketched a self-consistent system based on it.
With a set of atomic weights based on Cannizzaro's system, chemists had a scale according to which the elements could be placed in order. When placed in this order, properties of the elements recurred at various intervals. By the end of the 1860s, the first periodic classifications of the elements were proposed.
The selections of this section all pertain to the periodic system of elements. The work of J. A. R. Newlands shows the intellectual groping of a mind that recognizes the periodicity of elementary properties, but cannot quite formulate a self-consistent classification based on that periodicity. Dmitrii Mendeleev proposed the best known and most useful periodic system of the 1860s. The abstract in which that system first appeared in Western Europe and a review by Mendeleev of the periodic law 20 years later are included in this section. The last two selections treat the discovery of an element, argon, which had no place in the periodic table of the time and the effort to incorporate it into the periodic system.
The history of the periodic system is a fascinating one, full of priority disputes and polemics. Presenting that history in detail is not the purpose of the present section. For those interested in that history, I recommend van Spronsen 1969 and the multitudinous references therein. Van Spronsen names six co-discoverers of the periodic law: Alexandre Émile Beguyer de Chancourtois, Detlef Hinrichs, Julius Lothar Meyer, and William Odling in addition to Mendeleev and Newlands. I cannot agree with the claims for all six; however, van Spronsen provides sufficient detail to allow the reader to arrive at his or her own conclusion.
- Amedeo Avogadro, "Essay on a Manner of Determining the Relative Masses of the Elementary Molecules of Bodies, and the Proportions in Which They Enter into These Compounds," Journal de Physique73, 58-78 (1811), translated in Alembic Club Reprint No. 4, (Edinburgh, 1890); annotated excerpts.
- Stanislao Cannizzaro, Nuovo Cimento7, 321-366 (1858); translated as Alembic Club Reprint #18, Sketch of a Course of Chemical Philosophy by Stanislao Cannizzaro (1858) (Edinburgh: Alembic Club, 1910)
- J. W. van Spronsen, The Periodic System of Chemical Elements: a History of the First Hundred Years (Amsterdam: Elsevier, 1969)
- Charles-Adolphe Wurtz, "Account of the Sessions of the International Congress of Chemists in Karlsruhe, on 3, 4, and 5 September 1860," originally in Richard Anschütz, August Kekulé, 2 vols. (Berlin: Verlag Chemie, 1929) as Appendix VIII (pp. 671-88 of vol. 1); English translation by John Greenberg and William Clark published in Mary Jo Nye, The Question of the Atom (Los Angeles: Tomash, 1984)
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