Chemistry students and scientists alike use the periodic table of elements as a source for answers and new discoveries. It serves as much more than an educational cheat sheet; it’s composed of numerous bits and pieces of information about each chemical element and its properties, arranged in a precise methodical table that presents the patterns as they unfold across each row and column.
Since its creation in 1869, the periodic table has expanded tremendously. From the work of several different chemists and their discoveries it was organized by Dmitri Mendeleev, a Russian scientist who receives credit for the table’s creation, structure, and arrangement. The first discovered element, phosphorus (by German merchant Hennig Brand in 1649), and the work of Robert Boyle in the late 1600s formally began the research into the elemental substances – specifically, their properties, classifications, and nomenclature.
Prior to this time, little was known regarding the definition of an element. Aristotle loosly defined an element as a root from which all substances are made (however, it’s unclear if the world ‘element’ even existed in this time period). Plato eventually classified the four elements as earth, water, air, and fire.
This concept – both unclear and unsupported – went unchanged for the next hundreds of years. When potassium was discovered and used extensively in Boyle’s work in gases, however, new ideas began emerging. Throughout the 18th century the first basic elements were discovered, including oxygen, nitrogen, and hydrogen. French chemist Antoine Lavoisier put together a detailed list of 33 elements known at the time, differentiating between metal and non-metal.
He defined an element as a substance that cannot be broken down further, a definition that has remained for over 200 years. Lavoisier did, however, include light, caloric, and other compounds in his list which were later discounted. More elements were discovered, along with their atomic numbers. The letter abbreviations were introduced by Jons Jakob Berzelius in 1828.
During that same period, Johann Wolfgang Dobereiner classified the known elements for the first time based on their likeness and properties. He grouped certain elements in groups of three called triads; each element shared similar properties with the other two. Examples include lithium/sodium/potassium and chlorine/bromine/iodine.
Interestingly, each triad had numerically-ordered atomic numbers. Classification by atomic number, along with other properties, was explored and eventually used. In 1865, English chemist John Newlands divided all 56 known elements into 11 groups based on similar characteristics. With the numerous discoveries made up to that point, Dmitri Mendeleev began work on his periodic table.
With new elements discovered up until 1869 (by then, 63 had been discovered), it wasn’t until then when Mendeleev could present his work to the scientific community and the masses. He used a table to arrange the elements in order of increasing atomic mass but also incorporated molar mass and valencies (along with Newlands’ groups, cut down to eight). Pictured above, it was a very simple portrait of what is now used today. However, the overall ideas are unchanged.
He allowed for new elements to be added at any time and changes in element order to be made if research rendered it necessary, and although the table remains unchanged, several new discoveries have been incorporated, essentially expanding the table. One major discovery was of the noble gases by William Ramsay in 1894. They were initially tacked on as ‘Group 0’ but were later renamed ‘Group 8’ (or 18), causing a shift in groups.
In 1914, Henry Moseley modified the idea of atomic numbers based on nuclear charge rather than atomic weight, therefore causing a few changes in element order (such as argon before potassium, even though argon has a slightly larger atomic weight). Eventually, the table was reformatted to isolate transitional metals in their own group and subgroups. Each of the nine main groups were given their own name (alkali metals, halogens, etc.).
Throughout the 20th century numerous other elements were discovered. It wasn’t until 1940 when the first synthesized elements (i.e., plutonium) were created by chemist Glenn Seaborg. These were added to the periodic table as numbers 98 and above.
Today, the periodic table stands as an expanded version of the first creation by Dmitri Mendeleev, but it still retains the same basic properties, the same basic formatting, and is always open to new discoveries. It stands as one of science’s most well-known, ubiquitous creations and will be used in both laboratories and classrooms forever.
