Historical development and scientific impact of the periodic table

Periodic table provides a revolutionary system of classification of universally occurring elements. The existence of a few elements was documented since ancient Greece: gold, silver, copper, lead, and mercury were the most straightforward to understand and classify (Western Oregon University, 1997). During the Enlightenment, a renewed quest for scientific inquiry into the composition of matter was underway and aided by instruments that helped to discern the properties of discovered elements. A major breakthrough in elemental discovery was made in 1649, when German alchemist Hennig Brand discovered phosphorous after conducting experiments on urine: "He heated residues from boiled urine, and a liquid dropped out and burst into flames. This was the first discovery of phosphorus," (Lenntech, 2011). Over the next several hundred years, new elements were continually discovered. Researchers were then able to recognize similarities and differences between the elements that led to the development of a classification system. The classification system seemed headed towards one that was based on the atomic weight of each element.

However, it was not only atomic weight that gave rise to the Periodic Table. In 1817, Johann Dobereiner proposed a system of triads: groups of three elements that shared common properties such as chlorine, bromine, and iodine (Zumdahl & DeCoste, 2012). In 1864, John Newlands built upon the grouping system to propose octaves, a concept closely linked to the musical notation of octaves (Zumdahl & DeCoste, 2012). However, the Newlands octave system was not arbitrary: the English chemist observed that "certain properties seemed to repeat for every eighth element in way similar to the musical scale," (Zumdahl & DeCoste, 2012, p. 560). Finally, Russian chemist Dimitri Mendeleev developed the Periodic Table that provided more than just a system of classification. Mendeleev's table offered a system of ordered thinking whereby future elements that had yet to be discovered could be classified. Thus, the Periodic Table of Elements is a framework and a paradigm as much as it is a convenient chart of chemical elements.

In spite of a few flaws, Mendeleev's table of elements offered "the clearest, most consistent, and most systematic formulation, and Mendeleev made several testable predictions based on it," (Giunta, 1997). There was a fundamental principle that Mendeleev used to conceptualize the periodic table: which is sometimes referred to as Mendeleev's Periodic Law. Mendeleev's Periodic Law suggests that elements arranged according to their atomic mass "exhibit an evident stepwise variation of properties," and that "chemically analogous elements have either similar atomic weights," (Giunta, 1997). Chemical properties such as valence are also incorporated into the Periodic Law, to allow for the representation of a chart that not only accounts for existing discovered elements but also elements that have yet to be discovered. "For some mysterious reason, the elements are not just thrown together by nature in a jumble, but show very regular, astoundingly regular, patterns," (Wilker & Benedick, 2003, p. 119). Furthermore, Mendeleev noticed that the most common elements were the ones with the smallest atomic weights.

The relationship between atomic structure and the properties of the elements corresponds to their locations in the Periodic Table. The horizontal rows are the "periods," which correspond to atomic weight. The seven vertical columns in the arrangement correspond to groups of shared properties among all the elements contained therein. Mendeleev's original formulation has been altered, but the underlying concept remains the same. Basically, the elements are numbered according to their incremental increase in atomic mass: this is the concept of periodicity. The groupings, the columns, refer to their valency.

For example, Cooper (2007) points out that the second-to-last column in the Periodic Table is Group 17: Halogens. Halogens comprise a set of elements such as fluorine, chlorine, bromine, iodine, and astanine. The properties shared in common by these elements include their changing from gas to liquid, to unstable crystal "as their atomic weight increases," (Cooper, 2007, p. 28). Moreover, each of the halogens are diatomic molecules when occurring in nature: regardless of their state as being solid, liquid, or gas. "This happens because they all have seven electrons in their outermost shell," (Cooper, 2007, p. 29). They are all therefore highly reactive elements, and many of them are rare. All of the other columns in the Periodic Table can be thus understood: as groupings share in common properties that are often immediately apparent such as the noble gasses.