PRESENTATION OUTLINE
THE DEVELOPMENT OF THE PERIODIC TABLE
Antoine-Laurent de Lavoisier
Lavoisier wrote the first extensive list of elements containing 33 elements.
Distinguished between metals and non-metals which some of them was later shown to be compounds and mixtures. It contained a list of "simple substances" that Lavoisier believed could not be broken down further, which included oxygen, nitrogen, and hydrogen which were the basis of the modern periodic table.
Döbereiner developed 'triads', groups of 3 elements with similar properties.
Lithium, sodium & potassium formed a triad.
Calcium, strontium & barium formed a triad.
Chlorine, bromine & iodine formed a triad.
Alexandre-Émile Béguyer de Chancourtois
He was the first person to make use of atomic weights to reveal that the elements were arranged according to their atomic weights with similar elements occurring at regular intervals. He drew the elements as a continuous spiral around a cylinder divided into 16 parts. A list of elements was wrapped around a cylinder so that several sets of similar elements lined up, creating the first geometric representation of the periodic law.
JOHN ALEXANDER REINA NEWLANDS
Newlands was the first person to devise a periodic table of elements arranged in order of their relative atomic weights.[2] Continuing Johann Wolfgang Döbereiner’s work with triads and Jean-Baptiste Dumas' families of similar elements, he published in 1865 his 'Law of octaves', which stated that "any given element will exhibit analogous behaviour to the eighth element following it in the table." Newlands’ arranged all of the known elements into seven groups, which he likened to the octaves of music.
Mendeleev discovered the periodic table (or Periodic System, as he called it) while attempting to organise the elements in February of 1869. He did so by writing the properties of the elements on pieces of card and arranging and rearranging them until he realised that, by putting them in order of increasing atomic weight, certain types of element regularly occurred. For example, a reactive non-metal was directly followed by a very reactive light metal and then a less reactive light metal. Initially, the table had similar elements in horizontal rows, but he soon changed them to fit in vertical columns, as we see today.
In 1892 Ramsay’s curiosity was piqued by Lord Rayleigh’s observation that the density of nitrogen extracted from the air was always greater than nitrogen released from various chemical compounds. Ramsay then set about looking for an unknown gas in air of greater density, which—when he found it—he named argon. While investigating for the presence of argon in a uranium-bearing mineral, he instead discovered helium, which since 1868 had been known to exist, but only in the sun. This second discovery led him to suggest the existence of a new group of elements in the periodic table. He and his coworkers quickly isolated neon, krypton, and xenon from the earth’s atmosphere.
Mendeleev ordered his elements in order of their relative atomic mass, and this gave him some problems. For example, iodine has a lower relative atomic mass than tellurium, so it should come before tellurium in Mendeleev's table - but in order to get iodine in the same group as other elements with similar properties such as fluorine, chlorine and bromine, he had to put it after tellurium, so breaking his own rules. Using atomic number instead of atomic mass as the organizing principle was first proposed by the British chemist Henry Moseley in 1913, and it solved anomalies like this one. Iodine has a higher atomic number than tellurium.
