Monday, June 20, 2011

Division of Periodic Table

Long form of periodic table can be divided into four main blocks. These blocks are called s, p, d, & f. The divisions into four blocks depend upon the type of the orbital into which the last electron of atom has entered.
s – BLOCK 
The elements in which the last electron enters the s – subshell of their outer – most energy level are called s–Block elements. Since s–subshell can accommodate only two electrons so, s – block consists of only two groups i.e. group 1 and group 2. The general electronic configuration of s–block is ns1–2, where ‘n’ represents the outermost shell. The elements of group 1 are called Alkali Metals & group 2 is called Alkaline Earth Metals.
The general characteristics of s–Block elements are;
(i).          They are soft Metals.
(ii).         They are highly electropositive.
(iii).        They have low ionisation energies.
(iv).        They are very reactive & form ionic compounds.
(v).         They show oxidation state of +1 or +2.
(vi).        They are good reducing agents. 
p – BLOCK ELEMENTS
The elements in which the last electron enters the p–subshell of their outermost energy level are called p–Block elements. The exception is Helium (1S2). Since p–subshell can accommodate six electrons, so p–block consists of six groups i.e. 13, 14, 15, 16, 17, 18. Most of these elements are non-metals, some are metalloids and a few others are heavy elements which exhibit metallic character. The general configuration of p–block is ns2np1-6.
The general properties of p–block elements are;
(i).          They show variable oxidation states.
(ii).         They form ionic as well as covalent compounds.
(iii).        Most of them are non-metals.
(iv).        Most of them are highly electronegative.
(v).         Most of them form acidic oxides. 
d – BLOCK ELEMENTS
The elements in which last electron enters the d-sub-shell of the penultimate shell are called d-block elements since d-subshell can accommodate 10 electrons, so d-block consists of ten groups from 3 to 12. The general configuration is (n–1) d 1–10 ns 1–2, when ‘n’ is outer most shell. However, the exception is 46Pd (Palladium) whose configuration is 4d10 5s0, d-block consists of three complete rows and fourth is incomplete. The three rows are called First, Second and Third Transition Series.
The general characteristics of d-block elements are;
(i).          They are hard, high melting points.
(ii).         They show variable oxidation states.
(iii).        They form coloured complexes.
(iv).        They form ionic as well as covalent compounds.
(v).         Most of them exhibit paramagnetism.
(vi).        Most of them possess catalytic properties.
f – BLOCK ELEMENTS
The elements in which the last electron enters the f – subshell of anti-penultimate (third to the outer – most shell) shell are called f-block elements. Their general configuration is (n–2) f 1–14,     (n–1)d0–1, ns2, where n represents the outermost shell. They consist of two series elements each containing 14 elements placed at the bottom of the periodic table. The first series follow Lanthanium, La and is called Lanthanide Series or simply Lanthanides. The second series follow actinium, 89AC and are called Actinide Series or Actinides. 
The general characteristics of f – block elements are;
(i).          They show variable oxidation states.
(ii).         They are high melting metals.
(iii).        They have high densities.
(iv).        They form coloured compounds.
(v).         Most of the elements of Actinide series are radioactive.
Elements of s-block and p-block are called Representative Elements, elements of d-block are called Transition Elements and f-block elements are called Inner-Transition Elements.

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