TNPSC Free Notes Chemistry – Modern Periodic Table

இந்தக் கட்டுரையில், TNPSC குரூப் 1, குரூப் 2, குரூப் 2A, குரூப் 4 மாநிலப் போட்டித் தேர்வுகளான TNUSRB, TRB, TET, TNEB போன்றவற்றுக்கான  முறைகள் இலவசக் குறிப்புகளைப் பெறுவீர்கள்.தேர்வுக்கு தயாராவோர் இங்குள்ள பாடக்குறிப்புகளை படித்து பயன்பெற வாழ்த்துகிறோம்.

                             Modern Periodic Table

 In 1913, the English Physicist Henry Moseley, through his X-ray diffraction experiments,
proved that the properties of elements depend on the atomic number and not on the
atomic mass.
 Consequently, the modern periodic table was prepared by arranging elements in the
increasing order of their atomic number.
 This modern periodic table is the extension of the original Mendeleev’s periodic table
and known as the long form of periodic table.

Modern Periodic Law
The chemical and physical properties of the elements are the periodic functions of their atomic
numbers”.
Features of Modern Periodic Table
 .All the elements are arranged in the increasing order of their atomic number.
 The horizontal rows are called periods. There are seven periods in the periodic table.
 The elements are placed in periods based on the number of shells in their atoms.
 Vertical columns in the periodic table starting from top to bottom are called groups.
There are 18 groups in the periodic table.

 Based on the physical and chemical properties of elements, they are grouped into
various families.

Classification of elements into blocks
 We know that the electrons in an atom are accommodated in shells around the nucleus.
 Each shell consists of one or more subshells in which the electrons are distributed in
certain manner.
 These subshells are designated as s, p, d, and f. Based on the arrangement of electrons
in subshells, the elements of periodic
 Table are classified into four blocks namely s, p, d and f blocks.

s-Block Elements
 It includes group 1 (alkali metals) and group 2 (alkaline earth metals) elements. They are
also called as representative elements. The elements of group 1 (except hydrogen) are
metals.
 They react with water to form solutions that change the colour of a litmus paper from
red to blue.
 These solutions are said to be highly alkaline or basic. Hence they are called alkali
metals.
 The elements of group 2 are also metals. They combine with oxygen to form oxides,
formerly called ‘earths’, and these oxides produce alkaline solutions when they are
dissolved in water. Hence, these elements are called alkaline earth metals.
p-Block Elements

 These elements are in group 13 to 18 in the periodic table. They include boron, carbon,
nitrogen, oxygen, fluorine families in addition to noble gases
(Except helium). They are also called as representative elements.
 The p-block is home to the biggest variety of elements and is the only block that
contains all three types of elements: metals, nonmetals, and metalloids.
d-Block Elements
 It includes group 3 to group 12 elements. They are found in the centre of the periodic
table. Their properties are intermediate to that of s block and p block elements and so
they are called transition elements.
f – Block Elements
It includes 14 elements after (Lanthanum) La (57), called Lanthanoides and 14 elements after
(Actinium) Ac (89), called Actinoides. They are placed at the bottom of the periodic table. They
are also called as inner Transition elements.

Advantages of the Modern Periodic Table
 The table is based on a more fundamental property i.e., atomic number. It correlates
the position of the element with its electronic configuration more clearly.
 The completion of each period is more logical. In a period, as the atomic number
increases, the energy shells are gradually filled up until an inert gas configuration is
reached.
 It is easy to remember and reproduce. Each group is an independent group and the idea
of subgroups has been discarded.
 One position for all isotopes of an element is justified, since the isotopes have the same
atomic number.
 The position of the eighth group (in Mendeleev‘s table) is also justified in this table. All
transition elements have been brought in the middle as the properties of transition
elements are intermediate between left portion and right portion elements of the
periodic table.
 The table completely separates metals from non metals. The nonmetals are present in
upper right corners of the periodic table.
 The positions of certain elements which were earlier misfit (interchanged) in the
Mendeleev’s periodic table are now justified because it is based on atomic number of
the elements.
 Justification has been offered for placing lanthanides and actinides at the bottom of the
periodic table.

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