Class 11 Chemistry CLASSIFICATION OF ELEMENTS BASED UPON ELECTRONIC CONFIGURATION
On the basis of electronic configuration, the elements are of four types:
- Inert Elements
- Normal / Representative Elements
- Transition Elements
- Inner Transition Elements
- The atoms of these elements have completely filled shells. These elements belong to the 0 (zero) group of the periodic table.
- The elements are Helium(2He), Neon (10Ne), argon (18Ar), Krypton (36Kr), Xenon (54Xe), Radon (86Rn)
- All the elements have an electronic configuration as ns2np6; where n is the outermost shell
- Helium is the only element in this group which has the electronic configuration as 1s2.
- These elements do not participate in ordinary chemical reactions, as their outermost shells are completely filled. This is called the stable electronic configuration.
- These elements have the atoms in which all shells except the outermost shell is complete.
- The general electronic configuration of the atoms of these elements varies from ns1 to ns2np5, where n is the outermost shell.
- These elements are further classified as:
- s- block elements: The atoms of these elements have only s- electrons in their outermost shell. The elements of IA (known as alkali metals) and IIA (known as alkaline earth metals) sub-groups belong to this category. These elements lie on the extreme left of the periodic table. The alkali metals are Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs). The alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).
- p- block elements: These are the elements; whose atoms show progressive filling of p sub-energy level in the outermost shell. The number of electrons in the sub-energy level is 1-5. The elements of the sub-groups IIIA to VIIA belong to this group.
They are the elements with atoms in which two outermost shells are incomplete, whereas all the rest shells are complete.
The elements of the groups IB, IIB…………VIIB and VIII belong to this class. They are characterized by the regular filling of d-sub-energy level of their electronic configuration; therefore, they are also called as d- block elements. Thus, the atoms or ions of these elements contain partially filled d-orbitals. The regular filling of 3d, 4d, 5d or 6d sub-energy levels, there are four series of transition elements:
- First Transition Series (3d-series): In this series, there is a regular filling of the 3d sub-energy level. There are 10 elements; Scandium (21Sc) to Zinc (30Zn).
- Second Transition Series (4d- series): In this series, there is the regular filling of 4d sub-energy This series contains ten elements Yttrium (39Y) to Cadmium (48Cd).
- Third Transition Series (5d series): In this series, there is a regular filling of 5d sub-energy level. This series consists of 10 elements from Lanthanum (57La) to Mercury (80Hg). The 14 elements from Cerium (58Ce) to Lutetium (71Lu) are not included in this series, rather they are placed below the main part of the periodic table.
- Fourth Transition Series (6d series): In this series, there is a regular filling of 6d sub-energy level. This series is incomplete and contains seven elements from Actinium (89Ac) to Meitnerium (109Mt). Again, there are 14 elements that are excluded and placed below the main part of the table, these elements are Thorium (90Th) to Lawrencium (103Lw).
INNER TRANSITION ELEMENTS
The atoms of these elements have three incomplete outermost shells, whereas the rest of all the shells are complete. These elements are placed below the main part of the periodic table. There is a regular filling of f- sub-energy level, hence these elements are called f-block elements. These elements have been grouped into two series:
- Lanthanides: 14 elements (atomic numbers 58-71) between Lanthanum (57La) to Mercury (80Hg) are called lanthanides or rare-earth. In these elements, there is a regular filling of 4f sub-energy These elements are from Cerium (58Ce) to Lutetium (71Lu).
- Actinides: The elements between Actinium (89Ac) to Meitnerium (109Mt) are called actinides. There is a regular filling of the 5f-sub-energy These elements are from Thorium (90Th) to Lawrencium (103Lw).
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