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