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National Periodic Table Day is observed annually on February 7.

To understand the development of the periodic table, we first must understand the discovery of elements and their effect on science.

Elements known to ancient man were few. Gold, silver, copper, iron, lead, tin, mercury, sulfur and carbon were the earliest known elements. These were all known prior to the 1st century A.D.

Over time, arsenic, antimony, phosphorus and zinc were discovered. By 1809 there were 47 discovered elements.

One of the earliest attempts to organize the elements was by Johann Döbereiner in 1817. He organized elements into groups of three, or triads, based on similar qualities.

On February 7, 1863, English chemist John Newlands published one of the first table of elements, which divided the known 56 elements into 11 groups based on the “Law of Octaves.” This suggested that any one element will have similar properties to elements eight places before and behind it on the table.

Arranging the elements according to increasing atomic weight, Newlands was one of the first scientists to detect a pattern to the properties of elements. As a result, his table left room for new discoveries, predicting future discovered elements would complete the table. Newlands correctly predicted the discovery of Germanium.

While parts of Newlands periodic table had flaws, so did other later proposed tables. In 1869 chemist Dimitri Mendeleev published a paper developing a periodic table arranging the elements also based on atomic mass. By this time only 60 of the over 100 elements we know today were discovered.

There were also some inaccuracies attributed to some of those elements. While Mendeleev corrected some of these inaccuracies, he made assumptions about others causing elements to be placed incorrectly on the table. Like Newlands, Mendeleev predicted discoveries as well. He correctly predicted the properties of five elements and their compounds.

The discoveries throughout Scot William Ramsay’s career from 1892 to 1910, along with John William Strutt, Morris Travers and Frederick Soddy led to the identification of the noble gasses. Ramsay was awarded a Nobel Prize in 1904 for discovering five elements.

Henry Moseley, an experimental physicist, contributed to the development of the modern periodic table when he discovered in 1913 that each element has a specific number of protons. As a result, four new chemical elements were later found, though not during his lifetime.

Since the early 20th century there have been very few significant changes to the periodic table. The 21st century is still young, though and some researchers have suggested new approaches to the periodic table while maintaining its integrity as one of the most valuable tools in the science of chemistry. The current table tallies a total of 118 elements.


Visit for more information. Use #PeriodicTableDay to post on social media.

Educators, visit the National Day Calendar Classroom pages for ways to incorporate National Periodic Table Day into your classroom.

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