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Introduction
Development of Periodic Table
1. Dobereiner’s Law of Triads:
Concept Ladder
This law states that the atomic weight of
Doberenier's law of trids was
middle element is arithmetic mean of other
rejected because in some
two elements which are arranged such that triads all the three elements
the elements having similar properties are possessed nearly the same
placed in increasing order of atomic weight. atomic masses.
Atomic
Triad
Masses
Lithium 6.94
Sodium 22.99
Potassium 39.1 Previous Year’s Question
For ex. the atomic mass of sodium is almost Who is called the father of
equal to the arithmetic mean of the masses chemistry
of potassium and lithium i.e., 23.02. [AIPMT]
(1) Faraday
Ex Ca, Sr, Ba (2) Priestley
(3) Rutherford
P, As, Sb
(4) Lavoiser
Cl, Br, I
S, Se, Te
2. Newland’s Law of Octaves :
When elements arranged in order of their
increasing atomic weights, the properties of
Rack your Brain
every eighth element were similar to those of
the first one. Why was the law of octaves
discarded?
Periodic Table
1.
, sa re ga ma pa dha ni sa
Li Be B C N O F Na
Na Mg Al Si P S Cl K
3. Lother Meyer Curve
According to Lother Meyer if a graph is
between the atomic volume and atomic
weights of the elements and observed that
the elements with similar properties occupied
similar position on the curve. Concept Ladder
Lother Meyer proposed
that the physical
properties of the elements
are a periodic function of
the atomic weights.
(1) The most strongly electropositive alkali metal
occupy the peaks on the curve.
Rack your Brain
(2) The less strongly electropositive alkaline
earth metals occupy the descending position
Why Lothar Meyer's periodic
on the curve. classification was not that much
(3) The most electronegative elements i.e. appreciated.
halogens occupy the accupy the ascending
Periodic Table
position on the curve.
2.
,4. Mendeleev’s Periodic Table :
The physical and chemical properties of Definition
elements are the periodic function of their
A tabular arrangement of
atomic weights, i.e., when the elements are elements in rows and columns,
arranged in order of their increasing atomic highlighting the regular
weights, elements with similar properties repetition of properties of
elements is called a periodic
are repeated after certain regular intervals. It
table.
consists of seven horizontal rows called periods.
Mendeleev's original talb econsists of 8
vertical columns called groups. Thesea re Concept Ladder
numbered as I, II, III....VIII. However, 9th Modern Periodic Table
vertical column called zero group was added Mosley's Low
with the discovery of inert gases. Except for
a
Z
b
8 and 0, each group is further divided into
two sub-group designated as A and B. Group Z
8 consists of 9 elements arranged in three
sets each containing three elements.
Defects : Rack your Brain
Position of hydrogen, position of isotopes,
Iodine having lower atomic mass
position of lanthanides and actinides, anomalous
than tellurium was placed ahead
pairs of elements. Few similar elements are of tellurium. Why?
placed in different groups while some dissimilar
elements are grouped together.
Modern Periodic Law : Previous Year’s Question
y According to this law physical and chemical
The long form of periodic table has
properties of the elements are a periodic
[AIPMT]
function of their atomic numbers, i.e. elements (1) 8 horizontal rows & 7 vertical
are arranged in order of their increasing columns
atomic numbers, the elements with similar (2) 7 horizontal rows & 18 vertical
columns
properties are repeated after certain regular
(3) 7 horizontal rows & 7 vertical
intervals. columns
Cause of Periodicity : (4) 8 horizontal rows and 8 vertical
Periodic Table
It is due to repetition of similar outer electronic columns
configurations after certain regular intervals.
3.
, Periodic Table
4.
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