The periodic table is a chart of the chemical elements, ordered by their atomic number and electron configurations. The elements in each group (column) often have similar chemical properties. The table also shows four rectangular blocks with some similarities in physical and chemical properties. Six groups have generally accepted names, including the halogens of group 17 and the noble gases of group 18. The table provides a framework for analyzing chemical behaviour, and is extensively used in chemistry and other sciences. The Russian chemist Dmitri Mendeleev published the first widely recognized periodic table in 1869, and correctly predicted some properties of then-unknown elements that would be expected to fill in the gaps. Mendeleev's periodic table has been expanded and refined over time; elements 1–94 have all been found to occur naturally, and elements 95–118 have been synthesized in nuclear reactors or laboratories.
Read more: <https://en.wikipedia.org/wiki/Periodic_table> _______________________________ Today's selected anniversaries: 1697: Scottish student Thomas Aikenhead became the last person in Britain to be executed for blasphemy. <https://en.wikipedia.org/wiki/Thomas_Aikenhead> 1889: Statistician Herman Hollerith received a patent for his electric tabulating machine, the precursor to modern computers. <https://en.wikipedia.org/wiki/Herman_Hollerith> 1936: Reza Shah issued the Kashf-e hijab decree, ordering police to physically remove hijab from any woman in public. <https://en.wikipedia.org/wiki/Kashf-e_hijab> 1978: Harvey Milk was elected to the San Francisco Board of Supervisors, becoming the first openly gay man elected into public office in the United States. <https://en.wikipedia.org/wiki/Harvey_Milk> 2010: Gunmen from an offshoot of the Front for the Liberation of the Enclave of Cabinda attacked the bus transporting the Togo national football team to the Africa Cup of Nations, killing three. <https://en.wikipedia.org/wiki/Togo_national_football_team_attack> _____________________________ Wiktionary's word of the day: mendacity: 1. (uncountable) The fact or condition of being untruthful; dishonesty. 2. (countable) A deceit, falsehood, or lie. <https://en.wiktionary.org/wiki/mendacity> ___________________________ Wikiquote quote of the day: To bargain freedom for security is the devil's bargain. Having made the bargain, one enjoys neither freedom nor security. --Gerry Spence <https://en.wikiquote.org/wiki/Gerry_Spence> _______________________________________________ Wikipedia Daily Article mailing list. To unsubscribe, visit: https://lists.wikimedia.org/mailman/listinfo/daily-article-l Questions or comments? Contact [email protected]
