CBSE Class XI Chemistry Classification of Elements and Periodicity in Properties of Elements Concepts
CBSE important concepts for chapter - Classification of Elements and Periodicity in Properties of Elements in CBSE Class XI Chemistry. Based on CBSE and CCE guidelines. The students should read these basic concepts and practice the assignments to gain perfection which will help them to get more marks in CBSE examination.
Mandeleev’s Periodic Law:- The properties of the elements are the periodic function of their atomic masses. Moseley, the English physicist showed that atomic number is more fundamental property of an element than its atomic mass. Therefore, the position of an element in the periodic table depends on its atomic number than its atomic mass.
Modern Periodic Law: The physical and chemical properties of elements are the periodic functions of their atomic numbers.
Types of Elements: s-, p-, d- and f- blocks.
MAIN GROUP ELEMENTS/ REPRESENTATIVE ELEMENTS:
The s- and p- block elements are called main group elements or representative elements.
s- block elements: Group-1 (Alkali metals) and Group-2 elements (Alkaline earth metals) which respectively have ns1 and ns2 outermost electronic configurations.
p- Block elements: They belongs to group- 13 to 18. The outer most electronic configuration is ns2 np1-6. He (1s2) is a s- block element but is positioned with the group 18 elements (ns2 np6) because it has completely filled valence shell and as a result, exhibits properties characteristic of other noble gases.
d- block elements (Transition elements) are the elements of group 3 to 12 having outer electronic configuration (n-1) d1-10 ns1-2. Four transition series are 3d, 4d, 5d and 6d. The 6d- series is incomplete. Atomic radius generally decreases across a period and increases as we descend the group.
f-Block elements (Inner- transition Series) Lanthanoids charecterised by the filling of4 f-orbitals, are the elements following lanthanum from 58Ce to 71Lu. Actinoids characterised by filling of 5f-orbitals, are the elements following actinium from 70Th to 103Lr. Characteristic outer electronic configuration is (n-2) f1-14 (n-1) d0-1 ns2.
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