Elaboration of the Elements: Nineteenth-Century Advances in Chemistry, Electrochemistry, and Spectroscopy

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Elaboration of the Elements: Nineteenth-Century Advances in Chemistry, Electrochemistry, and Spectroscopy

Overview

By the end of the nineteenth century advances in electrochemical and spectroscopic methods, together with the discovery of elements exhibiting unique radioactive properties, worked to transform mankind's view of the cosmos on both the celestial and subatomic scale. By the end of the century the elements and matter comprising all things could no longer be viewed as immutable. Moreover, the rapid incorporation of the powerful properties of radioactive elements into medical practice established a course followed with increasing regularity and rapidity throughout the twentieth century. Although the composition and nature of radioactive elements was, at best, superficially understood, the practical benefits to be derived by society from their use forced their incorporation into technology far ahead of the pace of scientific understanding.

Background

The dramatic rise of scientific methodology and experimentation during the later half of the eighteenth century set the stage for the fundamental advances in chemistry and physics made during the nineteenth century. In less than a century, European society moved from an understanding of the chemical elements grounded in mysticism to an understanding of the relationships between elements found in a modern periodic table. During the eighteenth century laws against witchcraft were repealed, and near the close of the century an industrial revolution began to sweep across Europe. At the same time scientific disagreements became less grounded in religious disputes and more focused on differing interpretations of fundamental laws as they applied to practical inventions.

During the eighteenth century there was a steady march of discovery with regard to the chemical elements. Isolations of hydrogen and oxygen allowed for the formation of water from its elemental components. Nineteenth-century scientists built experiments on new-found familiarity with elements such as nitrogen, beryllium, chromium, and titanium.

Although a number of important discoveries took place with regard to elements during the eighteenth century, the nature of the interactions between elements continued to vex chemists. English scientist John Dalton's (1766-1844) explanation of chemical atomic theory at the beginning of the nineteenth century opened the door to a new understanding of chemistry based on the interactions of the elements. Subsequent nineteenth-century advances in electrochemistry provided chemists with powerful new tools of analysis and simultaneously dispelled the notion that simple electrostatic forces hold all elements together in compounds.

Advances in spectroscopy awaited further refinement of renowned English physicist Sir Isaac Newton's (1642-1727) postulates published in his 1704 work, Opticks, wherein Newton had described a rainbow of colors by passing sunlight through a prism (the principal component in the development of the spectroscope). At the dawn of the nineteenth century the "corpuscular" theory of light (i.e., that light was composed of particles) traveling through an "ether" still dominated scientific circles. English scientist William Wollaston (1766-1828) and Bavarian scientist Joseph Fraunhofer (1787-1826) laid additional foundations upon which subsequent nineteenth-century advances in spectroscopy arose by using prisms to investigate the colors emitted by various elements. Swiss mathematician Leonard Euler (1707-1783) set forth formulations for calculating the refraction of light using waves—each wavelength represented a particular color—that are still accepted as correct. In 1801 the publication of an experiment demonstrating the wave nature of light set the stage for a century-long battle over the duality of light (that it has both a wave and particle nature).

Impact

By the mid-nineteenth century, chemistry was in need of organization. New elements were being discovered at an increasing pace. Accordingly, the challenge for nineteenth-century chemists and physicists was to find a key to understand the increasing volume of experimental evidence regarding the properties of the elements. In 1869 the independent development of the periodic law and tables by the Russian chemist Dmitri Mendeleyev (1834-1907) and German chemist Julius Meyer (1830-1895) brought long-sought order and understanding to the elements.

Mendeleyev and Meyer did not work in a vacuum. English chemist J. A. R. Newlands (1837-1898) had already published several works that suggested the existance of relationships among families of elements, including his "law of octaves" hypothesis. Mendeleyev's periodic chart of elements, however, spurred important discoveries and isolation of chemical elements. Most importantly, Mendeleyev's table provided for the successful prediction of the existence of new elements, and these predictions proved true with the discovery of gallium (1875), scandium (1879), and germanium (1885).

By the end of the nineteenth century the organization of the elements was so complete that British physicists Lord Rayleigh (born John William Strutt, 1842-1919) and William Ramsay (1852-1916) were able to expand the periodic table and to predict the existence and properties of the noble gases argon and neon.

Nineteenth-century advances, however, were not limited to mere identification and isolation of the elements. By 1845 German chemist Adolph Kolbe (1818-1884) synthesized an organic compound, and in 1861 another German chemist, Friedrich Kekulé (1829-1896), related the properties of molecules to their geometric shape. These advances led to the development of wholly new materials (e.g., plastics and celluloids) that had a dramatic impact on a society in the midst of industrial revolution.

The most revolutionary development with regard to the elucidation of the elements during the nineteenth century came in the waning years of the century. In 1895 Wilhelm Röntgen (1845-1923) published a paper titled "On a New Kind of Rays." Röntgen's work offered the first description of x rays and offered compelling photographs of a human hand. The scientific world quickly grasped the importance of Röntgen's discovery. At a meeting of the French Academy of Science, Henri Becquerel (1852-1908) observed the pictures taken by Röntgen of bones in the hand. Within months Becquerel presented two important reports concerning "uranium rays" back to the Academy. Becquerel—who was initially working with phosphorescence—described the phenomena that later came to understood as radioactivity. Less than two years later two other French scientists, Pierre (1859-1906) and Marie Curie (1867-1934), announced the discovery of the radioactive elements polonium and radium. Marie Curie then set out on a systematic search for radioactive elements and was able, eventually, to document the discovery of radioactivity in uranium and thorium minerals.

As the nineteenth century drew to a close, Ernest Rutherford (1871-1937), using an electrometer, identified two types of radioactivity, which he labeled alpha radiation and beta radiation. Rutherford actually thought he had discovered a new type of x ray. Subsequently, alpha and beta radiation were understood to be particles. Alpha radiation is composed of alpha particles (the nucleus of helium). Because alpha radiation is easily stopped, alpha radiation-emitting elements are usually not dangerous to biological organisms (e.g., humans) unless the emitting element actually enters the organism. Beta radiation is composed of a stream of electrons (electrons were discovered by J. J. Thomson in 1897) or positively charged particles called positrons.

The impact of the discovery of radioactive elements produced immediate and dramatic changes in society. Within a few years, before the close of the century, high-energy electromagnetic radiation in the form of x rays, made possible by the discovery of radioactive elements, was used by physicians to diagnose injury. More importantly, the rapid incorporation of x rays into technology established a precedent increasingly followed throughout the twentieth century. Although the composition and nature of radioactive elements was not fully understood, the practical benefits to be derived by society outweighed scientific prudence.

Italian scientist Alessandro Volta's (1745-1827) discovery in 1800 of a battery using discs of silver and zinc gave rise to the voltaic pile or the first true batteries. Building on Volta's concepts, English chemist Humphry Davy (1778-1829) first produced sodium from the electrolysis of molten sodium hydroxide in 1807. Subsequently, Davy isolated potassium, another alkali metal, from potassium hydroxide in the same year. Lithium was discovered in 1817.

Throughout the nineteenth century the development and contribution of electrochemistry paralleled growing understanding of electrical phenomena. In 1834 English experimental chemist Michael Faraday (1791-1867) published "On Electrical Decomposition," in which he presented terms such as anion, cation, electrodes, anodes, and cathodes that persist in modern usage. A half-century later electrochemistry proved that it had progressed from novelty to primary research tool with the publication of Svante Arrhenius's (1859-1927) work on dissociation and electrolyte solutions. Not only did this work contribute to the development of acid-base chemistry, it also opened new avenues of biological and medical research.

Studies of the spectra of elements and compounds led to further discoveries. German chemist Robert Bunsen's (1811-1899) improvements to the famous laboratory burner that bears his name allowed for the development of new methods for the analysis of the elemental structure of compounds. Working with Russian-born scientist Gustav Kirchhoff (1824-1887), Bunsen made possible flame analysis (a technique now commonly known as atomic emission spectroscopy or AES) and established the fundamental principles and techniques of spectroscopy. Bunsen examined the spectra (i.e., component colors) emitted when a substance was subjected to intense flame. Bunsen's keen observation that flamed elements emit light only at specific wavelengths—and that each element produces a characteristic spectra—along with Kirchhoff's work on black body radiation set the stage for the subsequent twentieth-century development of quantum theory. Using his own spectroscopic techniques, Bunsen also discovered the elements cesium and rubidium.

Using the spectroscopic techniques pioneered by Bunsen, other nineteenth-century scientists began to deduce the chemical composition of stars. These discoveries were of profound philosophical importance to society because they proved that Earth did not lie in a privileged or unique portion of the universe. Indeed, the elements found on Earth—particularly those associated with life—were found to be commonplace in the cosmos.

In 1868 French astronomer P. J. C. Janssen (1824-1907) and English astronomer Norman Lockyer (1836-1920) used spectroscopic analysis to identify helium on the Sun. For the first time an element was first discovered outside the confines of Earth.

Spectroscopy gained wide use. In 1885 Swiss scientist Johann Balmer (1825-1898) set forth formulae that described the observed spectrum of hydrogen that Niels Bohr (1885-1962) subsequently used in the twentieth century to develop his model of the atom. In 1890 Dutch physicist Hendrick Lorentz (1853-1928) proposed that atoms produced visible light by oscillations. In 1896 another Dutch physicist, Pieter Zeeman (1865-1943), discovered a splitting of spectral lines in a gas subjected to a magnetic field (now termed the Zeeman effect).

Appropriate to the century that saw the development of evolutionary theory, nineteenth-century advancements in chemistry and the discovery of new elements—especially radioactive elements—profoundly changed the philosophical notions held since the ancient Greeks that the elements that comprised the cosmos, and all living things therein, were unchanging.

K. LEE LERNER