3.1.4 Periodicity - Classification of elements in s, p and d blocks
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The Periodic Table - Brief description
The Periodic Table is list of the chemical elements arranged into Groups (the columns going down) and Periods (the rows going across). The group number gives the number of valence (outer shell) electrons around the atom. The period number is the same as that of the outer energy shell.
Elements increase in atomic number across each period by one.
Calcium is in the 2nd group therefore it has 2 electrons in the outer shell and a valency of +II. It is in the fourth period therefore its outer electrons are in the fourth energy shell.
The blocks of the periodic table correspond to the last electron filled in these elements. For example, if the last electron is in a 3d orbital then that element is in the 'd' block:
Periodic table arrangement