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The history of the periodic table reflects over a century of growth in the understanding of chemical properties. The most important event was the publication of the first periodic table by Dmitri Mendeleev in 1869. While Mendeleev built upon earlier discoveries by such scientists as Antoine-Laurent de Lavoisier and Stanislao Cannizzaro, the Russian scientist is generally given sole credit for development of the periodic table.
The table is a visual representation of the periodic law which states that certain properties of elements repeat periodically when arranged by atomic number. The table arranges elements into vertical columns (groups) and horizontal rows (periods) to display these commonalities.
People have known about some chemical elements like gold, silver and copper from antiquity, as these are all found in nature in native form and are relatively simple to mine with primitive tools. However, the notion that there were a limited number of elements from which everything was composed originated with the Greek philosopher Aristotle. About 330 BC Aristotle proposed that everything is made up of a mixture of one or more of four "roots" (an idea originally put forth by the Sicilian philosopher Empedocles), but later renamed elements by Plato. The four elements were earth, water, air and fire. While the concept of an element was thus introduced, Aristotle's and Plato's ideas did nothing to advance the understanding of the nature of matter.
Hennig Brand was the first person recorded to have discovered a new element. Brand was a bankrupt German merchant who was trying to discover the Philosopher's Stone — a mythical object that was supposed to turn inexpensive base metals into gold. He experimented with distilling human urine until in 1649 he finally obtained a glowing white substance which he named phosphorus. He kept his discovery secret, until 1680 when Robert Boyle rediscovered it and it became public. This and related discoveries raised the question of what it means for a substance to be an "element".
In 1661 Boyle defined an element as a substance that cannot be broken down into a simpler substance by a chemical reaction. This simple definition actually served for nearly 301 years (until the development of the notion of subatomic particles), and even today is taught in introductory chemistry classes.
Lavoisier's Traité Élémentaire de Chimie (Elementary Treatise of Chemistry, 1789, translated into English by Robert Kerr) is considered to be the first modern chemical textbook. It contained a list of elements, or substances that could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulfur. It also forms the basis for the modern list of elements. His list, however, also included light and caloric, which he believed to be material substances. While many leading chemists of the time refused to believe Lavoisier's new revelations, the Elementary Treatise was written well enough to convince the younger generation. However, as Lavoisier's descriptions only classified elements as metals and non-metals, it fell short of a complete description.
In 1817, Johann Wolfgang Döbereiner began to formulate one of the earliest attempts to classify the elements. In 1828 he found that some elements formed groups of three with related properties. He termed these groups "triads". Some triads classified by Döbereiner are:
In all of the triads, the atomic mass of the second element was almost exactly the average of the atomic weights of the first and third elements.
By 1869, a total of 63 elements had been discovered. As the number of known elements grew, scientists began to recognize patterns in the way chemicals reacted and began to devise ways to classify the elements.
Alexandre-Emile Béguyer de Chancourtois, a French geologist, was the first person to notice the periodicity of the elements — similar elements seem to occur at regular intervals when they are ordered by their atomic weights. He devised an early form of periodic table, which he called the telluric helix. With the elements arranged in a spiral on a cylinder by order of increasing atomic weight, de Chancourtois saw that elements with similar properties lined up vertically. His chart included some ions and compounds in addition to elements. His paper was published in 1862, but used geological rather than chemical terms and did not include a diagram; as a result, it received little attention until the work of Dimitri Mendeleev.
Newlands noted that many pairs of similar elements existed which differed by some multiple of eight in mass number, and was the first person to assign them an atomic number. However, when his law of octaves was printed in Chemistry News, likening this periodicity of eights to the musical scale, it was ridiculed by some of his contemporaries. His lecture to the Chemistry Society on 1 March 1866 was not published, the Society defending their decision as they said such 'theoretical' topics might be controversial. The importance of his analysis was only recognised by the Chemistry Society with a Gold Medal some five years after they recognised Mendeleev. It was not until the following century, with Gilbert N. Lewis' valence bond theory (1916) and Irving Langmuir's octet theory of chemical bonding (1919) that the importance of the periodicity of eight would be accepted. The Royal Chemistry Society only properly acknowledged his contribution to science in 2008, when they erected a Blue Plaque on the house where he was born, which described him as the "discover of the Periodic Law for the chemical elements".
Dimitri Mendeleev, a Russian chemist, was the first scientist to make a periodic table much like the one we use today. Mendeleev arranged the elements in a table ordered by atomic mass, corresponding to relative molar mass as defined today. It is sometimes said that he played "chemical solitaire" on long train journeys using cards with various facts of known elements. On March 6, 1869, a formal presentation was made to the Russian Chemical Society, entitled The Dependence Between the Properties of the Atomic Weights of the Elements. His table was published in an obscure Russian journal but quickly republished in a German journal, Zeitschrift für Chemie (Eng., "Chemistry Magazine"), in 1869. It stated:
Scientific benefits of Mendeleev's table
Shortcomings of Mendeleev's table
Unknown to Mendeleev, Lothar Meyer was also working on a periodic table. Although his work was published in 1864, and was done independently of Mendeleev, few historians regard him as an equal co-creator of the periodic table. For one thing, Meyer's table only included 28 elements. Furthermore, Meyer classified elements not by atomic weight, but by valence alone. Finally, Meyer never came to the idea of predicting new elements and correcting atomic weights. Only a few months after Mendeleev published his periodic table of all known elements (and predicted some new elements to complete the table, plus some corrected atomic weights), Meyer published a virtually identical table. While a few people consider Meyer and Mendeleev the co-creators of the periodic table, most agree that, by itself, Mendeleev's accurate prediction of the qualities of the undiscovered elements lands him the larger share of credit. In any case, at the time Mendeleev's predictions greatly impressed his contemporaries and were eventually found to be correct.
An English chemist, William Odling, also drew up a table that is remarkably similar to that of Mendeleev, in 1864. Odling overcame the tellurium-iodine problem and he even managed to get thallium, lead, mercury and platinum in the right groups – something that Mendeleev failed to do at his first attempt.
In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
Thus Moseley placed argon (Z=18) before potassium (Z=19) based on their X-ray wavelengths, despite the fact that argon has a greater atomic weight (39.9) than potassium (39.1). The new order agrees with the chemical properties of these elements, since argon is a noble gas and potassium is an alkali metal. Similarly, Moseley placed cobalt before nickel, and was able to explain that tellurium occurs before iodine without revising the experimental atomic weight of tellurium (127.6) as proposed by Mendeleev.
Moseley's research also showed that there were gaps in his table at atomic numbers 43 and 61 which are now known to be Technetium and Promethium, respectively, both radioactive and not naturally occurring. Following in the footsteps of Dmitri Mendeleev, Henry Moseley also predicted new elements.
During his Manhattan Project research in 1943 Glenn T. Seaborg experienced unexpected difficulty isolating americium (95) and curium (96). He wondered if these elements more properly belonged to a different series, which would explain why the chemical properties of the new elements were different from expected. In 1945, against the advice of colleagues, he proposed a significant change to Mendeleev's table: the actinide series.
Seaborg's actinide concept of heavy element electronic structure, predicting that the actinides form a transition series analogous to the rare earth series of lanthanide elements, is now well accepted and included in the periodic table. The actinide series is the second row of the f-block (5f series). In both actinide and lanthanide series, an inner electron shell is being filled. The actinide series comprises the elements from actinium to lawrencium. Seaborg's subsequent elaborations of the actinide concept theorized a series of superheavy elements in a transactinide series comprising elements 104 through 121 and a superactinide series inclusive of elements 122 through 153.
The history of the periodic table is also a history of the discovery of the chemical elements. IUPAC suggests five "main discovery periods", and a sixth has been added here for very recently synthesised elements (discovered 2000 or later).
Seven elements can have their discovery traced to a tiny Swedish island near Stockholm. At a quarry and mine near the Swedish village of Ytterby on the island of Resarö, the rare earth mineral yttria was discovered (named after the village). This crude mineral eventually proved to be the source of four new elements that were named after the mineral ore and the village. These elements are yttrium (Y), erbium (Er), terbium (Tb), and ytterbium (Yb) and were first described in 1794, 1842, 1842, and 1878, respectively. In 1989 the ASM International society installed a plaque at the former entrance to the mine, commemorating the mine as a historical landmark. In addition, three other lanthanides, holmium (Ho, named after Stockholm), thulium (Tm, named after Thule, a mythic analog of Scandinavia), and gadolinium (Gd, after the chemist Johan Gadolin) also trace their discovery to the same quarry. On top of this, another rare earth element, scandium, is named after the Latin for Scandinavia, Scandia.
|Timeline of chemical elements discoveries|
industrial revolutions1800–1849 (+24 elements): science and
classifying elements received the impulse of the spectral analysis Boisbaudran, Bunsen, Crookes, Kirchhoff, and others "hunting emission line signatures"1850–1899 (+26 elements): the age of
1950–1999 (+16 elements): "post atomic bomb" issues for atomic numbers 98 and above (colliders, bombardment techniques)
2000–present (+5 elements): recent synthesis