Four blocks of elements in the periodic table.
1 – s block elements. Elements of groups 1 and 2 each possessing one and two electrons respectively in the s orbital of their outermost orbits are together known as s block elements.
Example : Na: 1s2 2s2 2p6 3s1 Mg: 1s2 2s2 2p6 3s2
Characteristics of s block elements.
a -They are metallic in nature and this character increases down each group.
b – They are highly electropositive in nature.
c – Most of them impart characteristic colors to the flame.
d – They generally do not exhibit variable valency.
e – The s block elements are present in groups 1 and 2.
2 – p block elements. Groups 13, 14, 15, 16, 17 and 18 form together p-block elements in which the- outermost energy levels have complete s orbitals while p orbitals have 1 to 6 electrons. The s, p and d orbitals of (n-1) orbit are completely filled.
Example : Cl: 1s2 2s2 2p6 3s2 2p5 O: 1s2 2s2 2p4
The s and p block elements are known as representative elements.
3 – d block elements. These are transition elements of groups 3 to 12 in the center of the periodic table. These contain generally electrons (sometimes only one) in the s orbital of the outermost energy level while their penultimate shell contain l to 10 electrons in d orbitals.
Example : Fe: 1s2 2s2 2p6 3s2 3p6 3d6 4s2 Sc: 1s2 2s2 2p6 3s2 3p6 3d2 4s2
Characteristics of d block elements.
a – These are metallic in nature and are called transition elements.
b – They generally form colored ions in solution.
c – They have tendency to show variable valency .
d – They have tendency to form complex compounds.
4 – f block elements. Lanthanides (At No. 57 to 71) actinides (At No. 89 to 103) are called f block elements. They generally contain 2 electrons in the s orbital of the outermost energy level, 1 electron in the d orbital of penultimate shell 1 to 14 electrons in the 4f or 5f orbitals.
Example : Ce: [Xe]4f1 5d1 6s2 Pr: [Xe]4f3 6s2
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