-
222
Introduction
Before written history, people were aware of some of the elements in the periodic table. Elements such as gold (Au), silver (Ag), copper (Cu), lead (Pb), tin (Sn), and mercury (Hg).
The history of the periodic table reflects over a century of growth in the understanding of chemical properties. The most important event in its history occurred in 1869, when the table was published by Dmitri Mendeleev, who built upon earlier discoveries by scientists such as Antoine-Laurent de Lavoisier. -
Jan 1, 1000
Propasal of the term "atom" - 400BC
Democritus and Leucippus propose the idea of the atom, an indivisible particle that all matter is made of -
Jan 2, 1000
360BC
Plato creates term ‘elements’ for the later development of the periodic table -
Discovery of Phosphorus - 1669
Hennig Brand attempted to created a Philosopher’s Stone, which is an object that could turn metals into gold. He heated residues from boiled urine, and a liquid dropped out and burst into flames. This was the first discovery of phosphorus. -
Categorisation - 1778
Antoine Lavoisier wrote the first extensive list of elements containing 33 elements & distinguished between metals and non-metals -
Elements grouped by similarities - 1780
The development of the periodic table begins with German chemist Johann Dobereiner, who grouped elements based on similarities. -
47 elements
In 1809 at least 47 elements have been discovered, and scientists began to see patterns in its characteristics. -
Grouping with similar properities - 1828
Johann Dobereiner developed groups of 3 elements with similar properties -
Law of Triads - 1829
John Dobereiner was a German scientist who developed the Law of Triads. Each triad was a group of three elements similar to each other. Alkali formers were grouped together, and so were salt formers. In 1829, he noticed that bromine, an element that fell about halfway between chlorine and iodine in atomic weight, also seemed halfway between them in its other properties. Other “triads” that he discovered were: calcium, strontium, and barium, and sulfur, selenium, and tellurium. -
Identified Elements - 1860
By 1860 about 60 elements were known. -
Octaves - 1863
John Newlands noticed that the second seven elements repeated the properties of the first seven closely, and he called them octaves. His law wasn’t taken too seriously, because the rest of the elements didn’t follow it. -
Arrangements through the valence - 1864
Lothar Meyer develops an early version of the periodic table, with 28 elements organised by the valence of the atom -
Discovery of Noble Gases - 1864
William Ramsay discovered the Noble Gases. He discovered neon, krypton, and xenon with Lord Rayleigh in 1864. He also isolated helium which had been observed in the spectrum of the sun but had not been found on earth. He ran Nitrogen across liquid Magnesium which resulted in a small amount of unreactive gas that later came to be known as Argon. In 1910 he made and characterised radon. -
Arranging by atomic weights - 1869
Russian chemist tDimitri Mendeleev proposed arranging elements by atomic weights and properties. Mendeleev's periodic table of 1869 contained 17 columns with two periods of seven elements each followed by two nearly complete periods. -
Mendeleev - 1869
Mendeleev realised that the periodic pattern didn’t apply to heavier elements. He decided to try to keep the pattern by saving spaces for elements that weren’t discovered yet. The gaps he focused on most were the gaps between aluminum and indium, silicon and tin, and born and yttrium. He called the elements that were unknown eka-aluminum, eka-silicon, and eka-boron, and predicted their characteristics. He published a paper where he demonstrated all known elements on a single periodic table. -
Mendeleev's Table - 1871
In 1871, Mendeleev published a form of periodic table, with groups of similar elements arranged in columns from I to VIII (1 to 8) He also gave detailed predictions for the properties of elements he had earlier noted were missing, but should exist. These gaps were subsequently filled as chemists discovered additional naturally occurring elements. -
Discovery of Radioactivity - 1886
Antoine Bequerel first discovered radioactivity. Ernest Rutherford named three types of radiation; alpha, beta and gamma rays. Marie and Pierre Curie started working on the radiation of uranium and thorium, which lead to the discoverey of radium and polonium. They discovered that beta particles were negatively charged. -
Electrons orbit - 1911
Rutherford and German physicist Hans Geiger discovered that electrons orbit the nucleus of an atom. -
X-Ray - 1913
In 1913, he used X-ray to order the elements. Each element has a unique emission pattern when X-rayed. Moseley used this to show that atomic number, not atomic weight was most important in grouping and ordering the elements. The problems with Mendeleev’s periodic table disappeared when atoms were positioned from lowest to highest atomic number. -
Discovery of protons - 1914
Rutherford first identified protons in the atomic nucleus. He also transmutated (an act that changes the form or character or substance of something) a nitrogen atom into an oxygen atom for the first time. English physicist Henry Moseley provided atomic numbers, based on the number of electrons in an atom, rather than based on atomic mass. -
Discovery of Lanthanides and Actinides - 1932
Glenn Seaborg identified lanthanides and actinides, which are usually placed below the periodic table. -
Discovery of Neutrons & Isotopes - 1932
James Chadwick first discovered neutrons, and isotopes were identified. In that same year Cockroft and the Walton first split an atom by bombarding lithium in a particle accelerator, changing it to two helium nuclei. -
Transuranic Elements - 1940
Glenn Seaborg synthesised transuranic elements (the elements after uranium in the periodic table) -
Conclusion
This is the modern periodic table that we all know of today. There is a possibility that new elements will be added if discovered.
