1. The properties of an element in the periodic table mainly depend on its outer electronic configuration, except in the case of transition elements.
2. Each period begins with an element having only one electron in the valence shell and ends with an element in which the valence shell is complete.
3. Number of electrons in the valence shell is equal to the group number e.g., chlorine has seven electrons in the valence shell and it is placed in the VIIth group. All elements in the same group have the same outer electronic structure, e.g., in VII A, fluorine, chlorine, bromine, iodine, astatine have seven electrons in the outermost shell. However, in the case of transition elements the number of electrons in the valence shell is not equal to the group number.
Remember:-
Position of Element in the Periodic Table
The position of an element in the periodic table is generally determined by its electronic configuration e.g. electronic configuration of sodium is 2, 8, 1 i.e., it has three shells and one electron in the outermost shell. Hence, it is placed in period number 3 and group number 1.However, in the case of transition elements this pattern is not followed.
