On 17 February 1869, Russian chemist Dmitri Mendeleev jotted down the symbols for the chemical elements, putting them in order according to their atomic weights and inventing the periodic table.

Dobereiner discovered that the relative atomic mass of the middle element in each triad was close to the average of the relative atomic masses of the other two elements. This gave other scientists a clue that relative atomic masses were important when arranging the elements.

Mendeleev’s table had organized the elements by their atomic mass. Moseley’s table had organized the elements by their atomic number. What do Mendeleev and Moseley’s period table have in common? They both organized their table from the lowest to the highest elements.

Like Thomson’s discovery of the electron, the discovery of radioactivity in uranium by French physicist Henri Becquerel in 1896 forced scientists to radically change their ideas about atomic structure. Radioactivity demonstrated that the atom was neither indivisible nor immutable.

An English scientist called John Newlands put forward his Law of Octaves in 1864. He arranged all the elements known at the time into a table in order of relative atomic mass. The pattern showed that each element was similar to the element eight places ahead of it.

In 1829, Johann Döbereiner recognised triads of elements with chemically similar properties, such as lithium, sodium and potassium, and showed that the properties of the middle element could be predicted from the properties of the other two.

Döbereiner’s triads
Döbereiner’s lamp
Johann Wolfgang Döbereiner/Known for

Mendeleev’s original table had the elements arranged in order of increasing atomic mass . Moseley organized his table in order of increasing atomic number .

Mendeleev arranged the elements in order of increasing relative atomic mass . When he did this he noted that the chemical properties of the elements and their compounds showed a periodic trend .

Like many scientists working at the end of the 19th-century the Russian chemist Dmitri Mendeleev (1834-1907) was looking for ways to organise the known elements. Mendeleev published his first periodic table of the elements in 1869. Features of Mendeleev’s tables. Mendeleev arranged the elements in order of increasing relative atomic mass.

Nevertheless, the basis of the modern periodic table was well established and even used to predict the properties of undiscovered elements long before the concept of the atomic number was developed. Ask most chemists who discovered the periodic table and you will almost certainly get the answer Dmitri Mendeleev.

In Mendeleev periodic table, vertical columns in the periodic table and horizontal row in the periodic table were named as groups and period respectively.

By the 1950s, versions of Deming’s table could be found in a majority of chemistry textbooks. Today, renderings of the table can be found on almost any type of consumer good—shower curtains, coffee mugs, key chains, phone covers, and the list goes on.