Periodic Classification PPT Chemistry Class 11

 Page 1


PERIODIC CLASSIFICATION OF 
ELEMENTS
Page 2


PERIODIC CLASSIFICATION OF 
ELEMENTS
1) Classification of elements :-
     The arranging of elements into different groups on the 
basis of the similarities in their properties is called 
classification of elements.
    The classification of similar elements into groups makes 
the study of elements easier. 
   There are about 114 different elements known so far.
  2) Early attempts at classification of elements :-
   a) The earliest attempt to classify elements was grouping 
the then known elements (about 30 elements) into two 
groups called metals and non metals.
       The defect in this classification was that it had no place 
for  metalloids (elements which have properties of both 
metals and non metals) which were discovered later.           
Page 3


PERIODIC CLASSIFICATION OF 
ELEMENTS
1) Classification of elements :-
     The arranging of elements into different groups on the 
basis of the similarities in their properties is called 
classification of elements.
    The classification of similar elements into groups makes 
the study of elements easier. 
   There are about 114 different elements known so far.
  2) Early attempts at classification of elements :-
   a) The earliest attempt to classify elements was grouping 
the then known elements (about 30 elements) into two 
groups called metals and non metals.
       The defect in this classification was that it had no place 
for  metalloids (elements which have properties of both 
metals and non metals) which were discovered later.           
b) Dobereiner’s Triads :-
    Dobereiner classified elements in the increasing order of 
their atomic masses into groups of three elements called 
triads. In each triad the atomic mass of the middle element 
was approximately equal to the average atomic mass of the 
other two elements.
   The defect in this classification was that all the then 
known elements could not be correctly arranged into triads. 
  
Triad Atomic mass Average atomic mass of 
I
st
 and 3
rd
element
Lithium          Li
Sodium          Na
Potassium     K
6.9
23.0
39.0
 22.95
Calcium         Ca
Strontium      Sr
Barium           Ba
40.1
87.6
137.3
88.7
Chlorine         CI
Bromine         Br
Iodine             I
35.5
79.9
126.9
81.2
Page 4


PERIODIC CLASSIFICATION OF 
ELEMENTS
1) Classification of elements :-
     The arranging of elements into different groups on the 
basis of the similarities in their properties is called 
classification of elements.
    The classification of similar elements into groups makes 
the study of elements easier. 
   There are about 114 different elements known so far.
  2) Early attempts at classification of elements :-
   a) The earliest attempt to classify elements was grouping 
the then known elements (about 30 elements) into two 
groups called metals and non metals.
       The defect in this classification was that it had no place 
for  metalloids (elements which have properties of both 
metals and non metals) which were discovered later.           
b) Dobereiner’s Triads :-
    Dobereiner classified elements in the increasing order of 
their atomic masses into groups of three elements called 
triads. In each triad the atomic mass of the middle element 
was approximately equal to the average atomic mass of the 
other two elements.
   The defect in this classification was that all the then 
known elements could not be correctly arranged into triads. 
  
Triad Atomic mass Average atomic mass of 
I
st
 and 3
rd
element
Lithium          Li
Sodium          Na
Potassium     K
6.9
23.0
39.0
 22.95
Calcium         Ca
Strontium      Sr
Barium           Ba
40.1
87.6
137.3
88.7
Chlorine         CI
Bromine         Br
Iodine             I
35.5
79.9
126.9
81.2
c) Newland’s octaves :-
   Newland classified the elements in the increasing order of their 
atomic masses into groups of eight elements called octaves like the 
notes of music. He found that when the elements were arranged in the 
increasing order of their atomic masses into octaves then there was 
similarity of properties in every eighth element.
   
    The defect in this classification was:-
 i) All the known elements and elements discovered later could not be 
correctly arranged into octaves.
 ii) Some elements having different properties were placed in the same 
rows like cobalt and nickel having different properties are placed along 
with Fluorine, Chlorine and Bromine. Iron having properties similar to 
Cobalt and Nickel are placed in different rows. 
sa re ga ma pa da ni
H LI Be B C N O
F Na Mg Al Si P S
Cl K Ca Cr Tl Mn Fe
Co 
and 
Ni
Cu Zn Y In As Se
Br Rb Sr Ce 
and 
La
Zr - -
Page 5


PERIODIC CLASSIFICATION OF 
ELEMENTS
1) Classification of elements :-
     The arranging of elements into different groups on the 
basis of the similarities in their properties is called 
classification of elements.
    The classification of similar elements into groups makes 
the study of elements easier. 
   There are about 114 different elements known so far.
  2) Early attempts at classification of elements :-
   a) The earliest attempt to classify elements was grouping 
the then known elements (about 30 elements) into two 
groups called metals and non metals.
       The defect in this classification was that it had no place 
for  metalloids (elements which have properties of both 
metals and non metals) which were discovered later.           
b) Dobereiner’s Triads :-
    Dobereiner classified elements in the increasing order of 
their atomic masses into groups of three elements called 
triads. In each triad the atomic mass of the middle element 
was approximately equal to the average atomic mass of the 
other two elements.
   The defect in this classification was that all the then 
known elements could not be correctly arranged into triads. 
  
Triad Atomic mass Average atomic mass of 
I
st
 and 3
rd
element
Lithium          Li
Sodium          Na
Potassium     K
6.9
23.0
39.0
 22.95
Calcium         Ca
Strontium      Sr
Barium           Ba
40.1
87.6
137.3
88.7
Chlorine         CI
Bromine         Br
Iodine             I
35.5
79.9
126.9
81.2
c) Newland’s octaves :-
   Newland classified the elements in the increasing order of their 
atomic masses into groups of eight elements called octaves like the 
notes of music. He found that when the elements were arranged in the 
increasing order of their atomic masses into octaves then there was 
similarity of properties in every eighth element.
   
    The defect in this classification was:-
 i) All the known elements and elements discovered later could not be 
correctly arranged into octaves.
 ii) Some elements having different properties were placed in the same 
rows like cobalt and nickel having different properties are placed along 
with Fluorine, Chlorine and Bromine. Iron having properties similar to 
Cobalt and Nickel are placed in different rows. 
sa re ga ma pa da ni
H LI Be B C N O
F Na Mg Al Si P S
Cl K Ca Cr Tl Mn Fe
Co 
and 
Ni
Cu Zn Y In As Se
Br Rb Sr Ce 
and 
La
Zr - -
3a) Mendeleev’s periodic law :-
       Mendeleev’s periodic law states that, ‘ The properties of 
elements are periodic functions of their atomic masses’.
A    B A    B A    B A   B A   B A   B A   B
Transition series