The periodic law suggests that elements arranged by atomic weight have similar characteristics at certain intervals. Dmitri Mendeleev formalized the law, but it was the result of a century of work by many scientists. The modern periodic table is a refined version of Mendeleev’s original chart. John Newlands and Alexandre-Emile Béguyer de Chancourtois also noticed repetitive properties. Mendeleev’s table aligned elements horizontally by atomic weight and vertically by similar properties, providing insight into a system of organization within chemistry.
The periodic law is one of the foundations of chemistry. The law suggests that elements, when arranged by atomic weight, tend to have similar characteristics at certain intervals from each other. The credit for formalizing the periodic law almost always goes to Dmitri Mendeleev, a Russian chemist. In truth, the discovery was the result of nearly a century of frantic work by a variety of scientists, all obsessed with determining properties and even discovering their own elements. The modern periodic table, a staple in every school science classroom, is actually a repeatedly refined and rearranged version of Mendeleev’s original chart.
During the 18th and 19th centuries, a new item seemed to crop up every week. With advanced chemical methods allowing for better examination of minute substances, the search for the elements became an endless hunt for many of the greatest scientists of the day. With such a profusion of items discovered and described, it soon became the concern of many to organize items into a list that made some sort of rational sense.
Elements are mainly described by a few distinctive characteristics: the number of protons in the nucleus, from which the atomic number is derived, mass calculations which define the atomic weight, and behavior. Many different attempts were made to arrange the elements so that each of these factors lined up in a reasonable way, but like a moving puzzle, every time one piece was put in order, the others got messy. The Periodic Law, a theory that would line up disparate information into an ordered table, seemed out of reach.
While Mendeleev rightfully deserves credit for the modern periodic table and for pulling all the strings together that form the periodic law, he wasn’t the first to try, by any means. John Newlands, an English chemist, noted the tendency for elements to behave similarly when aligned by atomic weight; in particular, every 8 intervals, a strange resemblance appeared. His “theory of octaves” likened the elements to the keys on a piano, where every eight keys form a repeating set. A French scientist, Alexandre-Emile Béguyer de Chancourtois, also noticed the repetitive properties and devised a table that arranged the elements in a helix shape. The work of both men has been largely ignored by the scientific community and Newlands has often been ridiculed for comparing him.
Mendeleev’s table illustrated the periodic law at a glance by aligning elements horizontally by atomic weight and vertically by similar properties. Thus the alkali metals lithium, sodium, potassium, rubidium, cesium, and francium form an orderly row along the left-hand side of the table, all remaining in order by atomic weight. Since not all elements were discovered at the time the tables were formed, Mendeleev simply left spaces in the table for those elements that should fit, according to his theory.
The Periodic Law provided insight into a system of organization within chemistry that had previously only been suspected. By transforming the organization of elements into a sorted table using the periodic law, Mendeleev made it obvious at a glance which elements shared which properties. Although the table was later remodeled and rearranged by British physicist John Moseley, Mendeleev’s inferences and theory remain largely unchallenged more than a century after his death.
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