The concept of periodic table blocks was given by Mendeleev. Dmitri Mendeleev published a table of elements, which states that the properties of elements are the periodic function of their atomic masses. With the passage of time, British chemist Moseley established that the fundamental property of elements which determine their physical and chemical properties is the atomic number and not atomic weight as proposed by Mendeleev. This led to a change in the periodic law stated above.Thus modern periodic law states that
|Properties of elements are the periodic functions of their atomic number.|
i.e., when elements are arranged in increasing order of atomic numbers, the properties of the elements are repeated after certain intervals
Periodic Table Blocks – s p d f block elements
Periodic table blocks have much importance in studying properties of elements. Depending upon the type of sub-shell in which their last electron being filled up in the atoms of the elements, the elements are divided into four blocks.
- The elements of groups 1 and 2 are known as s-block elements since in the atoms of the elements, s- subshell are being filled up.
- The elements of groups 13 to 18 are p-block elements since in the atoms of these elements p-subshell are being filled up.
- The transition elements are also called d-block elements because in the atoms of these elements d-subshell are being filled up.
- The other name of inner-transition elements is f-block elements because, in the atoms of these elements, f subshell is being filled up.
Blocks on the Periodic Table
Elements have been classified into four periodic table blocks (s, p, d, and f) depending upon the type of subshell which receives the last electron.The four periodic table blocks are:
s- block elements
|Elements in which the last electron enters in the s-orbitals of the valence shell of their atoms are called s-block elements.|
Since s-subshell can accommodate a maximum of 2 electrons, s-block consists of the elements of two groups, namely, group I (alkali metals) and group 2 (alkaline-earth metals). The general electronic configurations of the elements of group 1 and 2 are ns1 and ns2 respectively. These elements are present on the extreme left of the periodic table.
Example: Na: 1s2 ,2s2 ,2p6 ,3s1
- They are soft metals with low melting points and boiling points.
- These block elements have low ionization energy and are highly electron positive
- They are highly reactive and are good reducing agents.
- s Block elements have low electron affinity and electronegativity
- These metals and their compounds impart color to the flame.
For the depth knowledge of s block read the following subtopics:
p- block element
|Elements in which the last electron enters in the p-orbitals or subshell of the valence shell are called p-block elements.|
Since p-subshell can accommodate a maximum of 6 electrons, p-block consists of elements of six groups namely, 13, 14, 15, 16, 17 and 18 (except He). The general electronic configuration of p-block elements is ns2 np1-6 where n stands for the outermost shell, p-block elements are present on the extreme right of the periodic table.
Example: O (Z=8) = 1s2 ,2s2 ,2p6.
- They are gases (e.g., Cl2, F2, etc.). liquids (Br) and solids (Al, Sn, Sulphur, etc.).
- Have high ionization energy.
- They are electronegative in nature and this character decreases down a group.
- These elements are less metallic as compared to s-block elements.
- Their metallic character increases down a group but decreases across a period.
- Their reducing character decreases across a period while increases down a group.
d- block elements
|Elements in which the last electron enters in the d-orbitals of the penultimate (second last) shell of their atoms are called d-block elements.|
These elements consist of groups 3, 4, 5, 6, 7, 8, 9, 10, 11 and 12. They make up three complete rows of 10 elements and an incomplete fourth row in the periodic table. These elements are placed between s-block and p-block elements. Their general configuration ns1-2 (n-1) d1-10
Example Sc (Z = 21) = 1s2 . 2s2 2p6 3s2 3p6 3d1 4s2.
- They are hard metals with high melting points and boiling points.
- Show variable valency (oxidation state).
- Elements show magnetic properties.
- Elements can act as catalytic agents.
- Give colored compounds.
- They form complex compounds.
For the depth knowledge of d block read the following subtopics:
f- block elements
|Elements in which the last electron enters in the f orbitals of the antepenultimate (third from the last shell) of their atoms are called f-block elements.|
f block consists of two series of 14 elements each, known as lanthanide series and actinide series. These have been placed separately at the bottom of the periodic table. In the lanthanides, 4 f subshell and in actinides 5 f-subshell are being gradually filled up.
General electronic configuration of f block elements is (n–2)f1–14(n–1)d0–1ns2
- Lanthanides: [Xe]4f1–145d0–16s2
- Actinides: [Rn]5f1–146d0–17s2
Elements after uranium (atomic number 92) are called transuranic elements since they have been obtained from it through the nuclear reaction.
f-block elements are also called inner-transition elements because they form transition series within transition elements. The atoms of these elements have their three outermost shells incomplete.
- They are heavy metals with high m.pt. and b.pt.
- They give color to its compounds.
- Their show variable valency (oxidation state).
- These are mostly synthetic elements and are radioactive in nature.
For the depth knowledge of f block read the following subtopics:
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