Classification Of The Elements
- It is based on the type of orbitals which receives the differentiating electron (i.e., last electron).
- Based on the electronic configuration, elements can be classified into four types in the periodic table, viz s-block, p-block, f-block, and d-block elements.
- More than 70-80% of the known elements are metals.
- Elements located at the top of the periodic table are nonmetals and are less than 20. In a group, as the atomic number increases, the metallic character increases.
- In a period, there is a decrease in the metallic character from left to right.
- Also, the chemical, as well as the physical properties, vary with their atomic number.
- Elements of the same group exhibit similar chemical properties because of the similar valence shell electronic configuration
- When shells upto (n - 1) are completely filled and the last electron enters the s-orbital of the outermost (nth) shell, the elements of this class are called s-block elements.
- Group 1 & 2 elements constitute the s-block.
- General electronic configuration is [inert gas] ns1-2
- s-block elements lie on the extreme left of the periodic table.
- This block includes metals.
Group - IA or 1 Alkali metals
Group - II A or 2 , Alkaline earth metals
Summary of various trends in Periodic Table.
When shells upto (n -1) are completely filled and differentiating electron enters the p-orbital of the nth orbit, elements of this class are called p-block elements.
- Group 13 to 18 elements constitute the p-block.
- General electronic configuration is [inert gas] ns2np1-6
- p-block elements lie on the extreme right of the periodic table.
- This block includes some metals, all non-metals and metalloids.
- s-block and p-block elements are collectively called normal or representative elements.
Group - III A or 13, boron family :
Group - IV A or 14, carbon family :
Group - V A or 15, nitrogen family :
Group - VI A or 16 , Oxygen family :
When outermost (nth) and penultimate shells (n - 1)th shells are incompletely filled and differentiating electon enters the (n -1) d orbitals (i.e., d-orbital of penultimate shell) then elements of this class are called d-block elements.
- Group 3 to 12 elements constitute the d-block.
- General electronic configuration is [inert gas] (n - 1)d1-10 ns0-2
- d-block elements are classified into four series
- Series Elements (n-1)d being filled
- Those elements which have partially filled d-orbits in neutral state or in any stable oxidation state are called s transition elements.
- When n, (n-1) and (n -2) shells are incompletely filled and last electron enters into f-orbital of antepenultimate i.e., (n-2)th shell, elements of this class are called f-block elements., General electronic configuration is (n - 2)f1-14 (n - 1)d0-1 ns2
- All f-block elements belong to 3rd group.
- They are metals
- Within each series, the properties of the elements are quite similar.
- They are also called as inner-transition elements as they contain three outer most shell incomplete and were also referred to as rare earth elements since their oxides were rare in earlier days.
- The elements of f-block have been classified into two series:
- The actinides and lanthanides have been placed at the bottom of the periodic table to avoid the undue expansion of the periodic table.
1. Ist inner transition or 4 f-series, contains 14 elements 58Ce to 70Lu. Filling of electrons takes place in 4f subshell.
2. IInd inner transition or 5 f-series, contains 14 elements 90Th to 103Lr. Filling of electrons takes placed in 5f subshell.
Prediction of Period, Group and Block
- The block of an element corresponds to the type of subshell which receives the last electron.
- The group is predicted from the number of electrons in the valence shell or/and penultimate shell as follows.
(a) For s-block elements Group number = the no. of valence electrons.
(b) For p-block elements Group number = 10+ no. of valence electrons .
(c) For d-block elements Group number = no. of electrons in (n - 1) d sub shell + no. of electrons in valence shell.