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>
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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>
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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>
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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>