A. Mendeleev
Dmitri Mendeleev (1869, Russian)
1. Organized elements by increasing atomic mass.
2. Elements with similar properties were grouped together.
B. Moseley
Henry Mosely (1913, British)
1. Organized elements by increasing atomic number.
2. Resolved discrepancies in Mendeleev’s arrangement.
Properties of Te & I were different from other elements in the column in Mendeleev’s table
They “fit” when arranged by atomic number.
Periodic Law
When elements are arranged in order of
increasing atomic #, elements with similar
properties appear at regular intervals.
Families of Elements
Similar valence e- within a group result in
similar chemical properties
ss11
ss22
ss22pp66
ss22pp55ss22pp44
s2p1ss22pp22
ss22pp33
End in dEnd in dxx
Families of Elements
Alkali MetalsAlkaline Earth MetalsTransition MetalsHalogensNoble Gases
Lanthanides (57-70)Actinides (89-102)