(In the modern periodic table, a group or family corresponds to one vertical column. The periodic table allows chemists a shortcut by arranging typical elements according to their properties and putting the others into groups or families with similar chemical characteristics. h hydrogen 1 1.0079 li lithium 3 6.941 na sodium 11 22.990 k potassium 19 39.098 rb rubidium 37 85.468 cs cesium 55 132.91 fr francium 87 (223) be beryllium 4 9.0122 mg magnesium 12 24.305 ca calcium 20 40. Were it not for the simplification provided by this chart, students of chemistry would need to learn the properties of all 118 known elements. The term “periodic” is based on the discovery that elements show patterns in their chemical properties at certain regular intervals. Mendeleev left spaces for elements he expected to be discovered, and today’s periodic table contains 118 elements, starting with hydrogen and ending with oganesson, a chemical element first synthesized in 2002 at the Joint Institute for Nuclear Research (JINR) in Dubna, Russia, by a team of Russian and American scientists. Periodic Table of the Elements Chemistry Reference Sheet California Standards Test Sodium 22.99 Na 11 Atomic number Element symbol Average atomic mass Element name Hydrogen 1.01 H 1 Lithium 6.94 Li 3 Sodium 22.99 Na 11 Potassium 39.10 19 K Nickel 58.69 Ni 28 Rubidium 85.47 Rb 37 Rutherfordium (261) Rf 104 Molybdenum 95.94 Mo 42 Germanium 72.61. Its story is over 200 years old, and throughout its history, it has been a subject for debate, dispute and alteration.Īttempts to classify elements and group them in ways that explained their behavior date back to the 1700s, but the first actual periodic table is generally credited to Dmitri Ivanovich Mendeleev, a Russian chemist who in 1869 arranged 63 known elements according to their increasing atomic weight. Go into any scientist’s office or lecture hall anywhere in the world and you are likely to see one. There is no more enduring reflection of science than the Periodic Table of Chemical Elements, which sheds light not only on the essence of chemistry but physics and biology as well.
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