Periodic Table of Elements

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1. Atoms are arranged in order of atomic masses.
2. Mendeleev left empty spaces for undiscovered elements. He also predicted properties of those elements which later proved to be quite accurate.

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1. Elements in each group (column) show similar electron configurations which explain the similarity of properties of elements within the group.
2. Consists of 7 rows (period) and 18 columns (group). note: there are 2 separated rows which are inner-transition elements.
3. Positions of elements in the periodic table are determined by the valence-shell configuration or valence electrons.
   1. The highest principle quantum number (n) indicates the row (period) number of the element.
   2. The number of valence electrons indicates the group number of main groups elements.

1. Alkali metals (group 1A)
2. Alkaline Earth metals (group 2A)
3. Halogen (group 7A)
4. Noble gas (group 8A)
5. Born family (group 3A)
6. Carbon family (group 4A)
7. Nitrogen family (group 5A)
8. Oxygen family (group 6A)

1. group 1B-8B
2. Inner-transition metals: Lanthanide and Actinide series.