The United Nations General Assembly during its 74th Plenary Meeting proclaimed 2019 as the International Year of the Periodic Table of Chemical Elements. The initiative for IYPT2019 is supported by IUPAC in partnership with the International Union of Pure and Applied Physics (IUPAP), European Association for Chemical and Molecular Science (EuCheMS), the International Council for Science (ICSU), International Astronomical Union (IAU), and the International Union of History and Philosophy of Science and Technology (IUHPS).
1869 is considered as the year of discovery of the Periodic System by Dmitri Mendeleev. Russian chemistry professor Dmitri Mendeleev and German chemist Julius Lothar Meyer independently published their periodic tables in 1869 and 1870, respectively.Mendeleev’s table, dated March 1, 1869, was his first published version. That of Meyer was an expanded version of his (Meyer’s) table of 1864. They both constructed their tables by listing the elements in rows or columns in order of atomic weight and starting a new row or column when the characteristics of the elements began to repeat.
In celebration of the periodic table’s 150th anniversary, the United Nations declared the year 2019 as the International Year of the Periodic Table, celebrating “one of the most significant achievements in science”.
Structure of Periodic Table:
The current table holds 117 elements in a very distinct order for the purpose of showing similarities and differences in chemical properties. 94 are found in nature and the other 24 were synthetically produced with particle accelerators. Elements are placed in order of increasing atomic number, which is the number of protons in the nucleus of the element’s atom. The rows are also organized so that elements with similar properties are found in the same columns. At the bottom of the periodic table is a two row block of elements that contain the lanthanoids and actinides. These groups are classified as inner transitional metals.
Classification in Periodic Table:
1. The chemical elements classified into groups, periods, and blocks.
2. Groups are the vertical columns located on the periodic table. Many groups contain elements with very similar properties.
3. Periods are made up of the horizontal rows of the table.
4. Like Groups, periods also contain specific trends in similar properties.
5. Blocks are important as different regions of the periodic table due to the outer shell of electrons within the elements’ atoms. The blocks of the periodic table include the s-block, p-block, d-block, and f-block.
1. Properties of an element can actually be predicted based on its table location. Trends within groups are explained by common electron configuration in their valence shells.
2. From the top of the group to the bottom, atomic radii of the elements increase.
3. Moving from the left of the periodic table to the right, atomic radii decreases which causes the ionization energy to increase.
4. Moving left to right, electro-negativity and electron affinity increase.