The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number (number of protons),electron configurations, and recurring chemical properties. This ordering shows periodic trends, such as elements with similar behavior in the same column. It also shows four rectangular blocks with some approximately similar chemical properties. In general, within one row (period) the elements are metals on the left, and non-metals on the right.
The rows of the table are called periods; the columns are called groups. Six groups (columns) have names as well as numbers: for example, group 17 elements are the halogens; and group 18, the noble gases. The periodic table can be used to derive relationships between the properties of the elements, and predict the properties of new elements yet to be discovered or synthesized. The periodic table provides a useful framework for analyzing chemical behavior, and is widely used in chemistry and other sciences.
All elements from atomic numbers 1 (hydrogen) to 118 (ununoctium) have been discovered or synthesized, with the most recent additions (elements 113, 115, 117, and 118) being confirmed by the IUPAC on December 30, 2015.[1] The first 94 elements exist naturally, although some are found only in trace amounts and were synthesized in laboratories before being found in nature.[n 1] Elements with atomic numbers from 95 to 118 have only been synthesized in laboratories or nuclear reactors.[2] Synthesis of elements having higher atomic numbers is being pursued. Numerous synthetic radio nuclides of naturally occurring elements have also been produced in laboratories.
Henry Gwyn Jeffreys Moseley (23 November 1887 – 10 August 1915) was an Englishphysicist, whose contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra. Moseley's Law justified many concepts in chemistry by sorting the chemical elements of the periodic table of the elements in a logical order based on their physics.
Moseley's law advanced atomic physics by providing the first experimental evidence in favour of Niels Bohr's theory, aside from the hydrogen atom spectrum which the Bohr theory was designed to reproduce. That theory refined Ernest Rutherford's and Antonius van den Broek's model, which proposed that the atom contains in its nucleus a number of positive nuclear charges that is equal to its (atomic) number in the periodic table. This remains the accepted model today.
When World War I broke out in Western Europe, Moseley left his research work at theUniversity of Oxford behind to volunteer for the Royal Engineers of the British Army. Moseley was assigned to the force of British Empire soldiers that invaded the region ofGallipoli, Turkey, in April 1915, as a telecommunications officer. Moseley was shot and killed during the Battle of Gallipoli on 10 August 1915, at the age of 27. Experts have speculated that Moseley could have been awarded the Nobel Prize in Physics in 1916, had he not been killed. As a consequence, the British government instituted new policies for eligibility for combat duty.
