Modern periodic table is based on a law such as
The physical and chemical properties of element are the periodic function of their atomic numbers. i.e. if the elements are arranged in terms of increasing order then an elemental pattern is formed.
The arrangement of modern periodic table consist of :
1. Seven Horizontal Rows, called periods or series.
2. Eighteen vertical columns, called groups or families.
The periods of modern periodic table are named as Mendeleev's periodic table but the elements of a period are arranged in a long extended form with the gradual increase of atomic number.
1. IA, IIA, IIIA, IVA, VA, VIA, VIIA
2. IB, IIB, IIIB, IVB, VB, VIB, VIIIB
3. VIII, it consist of three vertical columns
4. Zero groups, it consist of inert gases
C. Lanthanides and Actinides at the bottom of the periodic table
In the sixth period, the elements with atomic number 58 to 71 have been grouped with lanthanum and are called lanthanides or rare earth. Similarly in the seventh period, elements with atomic number 90 to 103, have been grouped with actinium and these are called actinides.
1. Elements with atomic number 57 resemble elements with atomic number 58 to 71 in their properties. Also elements with atomic number 89, resembles elements with atomic number 90 to 103 in their properties.
2. The undue expansion of the periodic table is avoided.
D. Types of elements of the periodic table
The modern classification of elements in terms of atomic number is an electronic basis and on the basis of the electronic configuration of the incompletely filled orbitals, the elements have been divided into three types with four blocks- s, p, d and f blocks.
a. Representative or s- or p-block elements
b. Transition or d-block elements
c. Inner transition or f-block elements
(a) Representative elements
It includes elements with atoms which have their outmost shells incomplete. The electronic configuration of the incomplete shells is either ns to the power 1 or 2 or ns to the power 2 and np to the power 1 to 6. These are assigned to zero group and consist of noble gases. These are the elements of group IA and IIA. Elements of this group
1. are present on the extreme left of the periodic table
2. are highly active electropositive and reducing agents
3. impart color to the flame(except Be and mg)
Elements of group IIIA to VIIA have 1 to 5 electrons in their p-subshell and are called p-block elements.
1. They are present on the right of periodic table.
2. Include highly electronegative elements
(b) Transition or d-block elements
(1) First transition series : It includes 10 elements with atomic number 21 to 30
(2) Second transition series: It includes with atomic number 39 to 48
(3) Third transition series: It includes elements with atomic number 57, 72 to 80.
(4) Fourth transition series:
It includes elements with atomic number 89, 104, 105 and 106 to 110
(c) Inner transition or f-block elements:
It includes elements which have three outer most shells incomplete and by Aufbau principle, correspond to filling up of 4f and 5f orbitals. These are called inner transition elements because these have not only incomplete d sub-shell but also incomplete f sub-shell. These are called rare earths because their compounds are available in small quantities. These are placed as two separate groups on the bottom of the modern periodic table. Lanthanides belong to group IIIB and sixth period of the periodic table whereas actinides belong to group IIIB and seventh period of the periodic table. Most of these elements are radioactive and resemble d-block elements in their chemical properties.