Evolution of the Periodic Table: From Triads to Actinides

Classified in Chemistry

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Properties of Metals:

Shiny, lustrous, can be polished, strong, and solid.


Dull, not lustrous, cannot be polished, weak, half are gases.

18 Families or Groups, 18 Periods:

Elements in the same group have common characteristics. Horizontal is period, vertical is family or group.

Periodic Law:

The PT is organized by atomic number Z. Elements with similar properties are in the same family.

Properties of Metalloids:

Have characteristics of metals and nonmetals. Located between metals and nonmetals.

Johann Dobereiner (1829):

Classified elements into groups of three, called triads.

John Newlands (1838-1898):

Law of Octaves (1863) suggested arranging elements in octaves.

Dmitri Mendeleev (1834-1907):

Published a table of elements organized by increasing atomic mass.

Lothar Meyer (1830-1895):

Published his own table of elements organized by increasing atomic mass.

Henry Moseley (1887-1915):

Rearranged elements by increasing atomic number in 1913.

Glenn T. Seaborg:

Moved 14 elements to the actinide series after discovering 10 new elements in 1944.

Noble Gases:

He, N, O, F, Ne, Cl, Ar, Kr, Xe, Rn, H. Transition Metals: Sc, Ti, V, Cr, Mn, Fe, Co, Cu, Zn. More Metals: C, P, S, Se, I, Uus, Lv, Bi, In. No Lo Se: Br, Hg. Elements in the same period have a common main energy shell.

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