CBSE Class 12 Chemistry Notes: Periodic Properties – Modern Periodic Law (Electronic Configuration of Elements)

Long Form of the Periodic Table and Electronic Configuration of Elements:

Classification Of Elements On The Basis Of Their Electronic Configuration

On the basis of electronic configuration, the elements may be divided into four groups, that is s, p, d & f. This division is based on the name of orbital which receives the valence electron.
s- Block elements:
Elements in which the last electron enters the s- orbital or their respective outermost shells are called s- block elements. These are present in the left part of the periodic table in group IA & IIA i.e. 1 & 2 group in modern periodic table. Electronic configuration of valence shell is ns^1-2 (n 1 to 7)

Characteristic of s block elements:

• They are soft metals with low melting & boiling points
• They posses metallic character & reactivity of metal increases down the group
• They are highly electropositive and having low ionization enthalpies
• They have valency +1(in case of alkali metals) &+2 (in case of alkaline earth metals)
• Most of the metals of this block impart characteristic color to the flame
• They are strong reducing agents & are good conductor of heat & electricity.

p block elements:
These are present in right part of the periodic table and constitute the groups IIIA to VIIA and zero groups i.e. group 13 to 18 of the modern periodic table. Most of these elements are metalloids & non metals but some of them are metals also. The last electron enters in p  orbital of valency shell and electronic configuration of valency shell is ns² n^1-6(n=2 to 7)

Characteristics of p block elements:

• It contains both metals & non metals. The metallic character decrease from left to right along the period and metallic character increases from top to bottom within a group
• They mostly form covalent compounds
• Ionization energy is higher as compared to s – block elements.
• Reducing character increases from top to bottom in a group & oxidizing character increases left to right in a period.

d- Block elements:

These are present in the middle part of the periodic table (between s & p block elements) and constitute IIIB to VIIB, VIII, IB & IIB i.e. 3 to 12 groups of the modern periodic table. The outermost electronic configuration is (n-1) d^1-10 ns^1-2 (n=4 to 7). There are four series of d-block elements, which are 3d series – Sc (21) to Zn (30) 4d series – Y( 39) to Cd(48) & 5d series – La (57), Hf (72) to Hg(80) 6d series Ac(89), Rf(104) Unb (ununbium) 112 (incomplete)

Characteristics of d – block elements:

• These are hard, ductile & malleable metals with high melting & boiling points
• Ionization energy is between s & p- block elements
• They show variable oxidation states and are good conductors of heat & electricity.
• They form both ionic & covalent compounds and compounds are generally coloured and paramagnetic in nature
• Most of the transition metals form alloys.

f- Block elements:
These are placed separately below the main periodic table and are mainly related to IIIB i.e. group 3 of the periodic table. There are two series of f–block elements, which are
4f series – Lanthanides 14 elements Ce(58) to Lu(71) and 5f series Actinides 14 elements Th(90) to Lr(103). Their outermost electronic configuration is (n-2)f^1-14 (n1)s²(n-1)p⁶ (n-1) d^0-1 ns².
(n = 6 & 7)

Characteristics to f – block elements:

• They are heavy metals with high melting & boiling points
• They show variable oxidation states & their compounds are generally coloured
• Most of the elements of the actinide series are radioactive

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