Periodic Table

Devised by Dmitri Mendeleev in 1868. It clearly shows the relationship between all of the elements and allowed the existence of elements to be predicted before they were discovered.

  • They are listed according to the number of protons in their atom.
  • Rows from left to right are periods. Period number is the highest unexcited energy level for an electron of that element.
  • Columns are groups.
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra Ac
Lanthanides Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Actinides Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr

  • There are 90 elements in the periodic table that occur in nature.
  • Technetium was the first element to be made artificially.

Historical Notes

  1. 1808 Dalton published a periodic table based on atomic weights.
  2. 1869 Mendeleyev used a periodic table of known elements to correctly predict the properties of then undiscovered elements.

See also: Actinide, Alkali Metal, Alkaline Earth Metal, Atomic Number, Chemical Symbols, Congener, Element Symbol, Group, Halogen, Lanthanide, Mendeleev, Dmitri Ivanovich, Periodic Law, Periodic Trend, Rare Earth Element, Transition Metal.

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Subjects: Chemistry