Dobereiner (1780-1849)

The german chemist who is known for work that foreshadows the periodic law for the chemical elements.

• arranged the 1st periodic table by triads (similar properties)

• 1829 proposed law of triads - middle element in the triad had atomic weight that was the average of the pother 2 (this idea expanded beyond triads)

Dmitri Mendeleev (1834-1907)

father of the periodic table***

• arranged the periodic table by atomic mass and recognized gaps for elements that had yet to be discovered

• where a gap existed there was predicted to be a new element would be found and assume its properties

Henry Moseley (1887- 1915)

english physicist who arranged his periodic table by atomic number and is now known as the modern periodic table.

• 1913: atomic numbers were not arbitrarily assigned

• redefine the idea of atomic numbers into real and objective whole-number quantity (protonos)

PERIODIC LAW: elements are arranged in increasing atomic number; physical and chemical properties show periodic pattern (elements in each group have similar properties

HYDROGEN STANDS APART: 1 valence electron is very reactive but loses 1 electron rather quickly more similar to nonmetals than to metals.

Cation: A positively charged ion that is formed when an atom loses one or more electrons

Anion: a negatively charged ion that is formed when an atom gains one or more electrons

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