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Rupinder , asked a question
Subject: Science , asked on 29/1/15

what are the limitations of mendeleevs periodic table

Satyajit Mohanty , added an answer, on 4/2/11
423 helpful votes in Science

Hi Snoby.. !!!!

Limitations are :

Position of hydrogen : Hydrogen is placed in Group IA. However, it actually resembles the elements of Group-IA (alkali metals ) as well as the elements of Group VII-A (halogens ). Thus, the position of hydrogen in the periodic table is not clear.

Position of isotopes : On the basis of atomic weight , various isotopes of the same elements should be assigned different places in the periodic table. Mendeleev could not provide separate places for isotopes.

Position of lanthanides and actinides : Fourteen elements following Lanthanum(known as lanthanides or rare earths) and the fourteen elements following Actinium (known as actinides or transuranic elements ) have not been provided separate and proper places in the Mendellev's table, rather they have been placed in two rows at the bottom of the table.

Disimilar elements placed together : Noble metals like Cu, Ag and Au are placed along with chemically dissimilar alkali metals in Group I . Similarly, Mn possessing very few similarities with halogens have been placed in VII group.

Similar elements separated : In Mendeleev's periodic table, certain chemically similar elements such as copper and mercury ; gold and platinum have been placed in different groups.

Anomalous pairs : In the Mendeleev's Table based on atomic weight, the positions of certain pairs , e.g. Argon( at. wt = 39.94) and potassium ( at. wt = 39.1) : Cobalt( at wt =58.93 ) and nickel ( at wt = 58.71 ) ; Tellurium at wt = 127.60) and iodine (atomic weight = 126.90 ) would be reversed. In other words, certain pairs of elements are misfit in the periodic table, if atomic weight is the basis of classification.

Hope this helps !!!!!!

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Pranshu Chakrawarti , added an answer, on 29/1/15
9 helpful votes in Science
1) The position of Hydrogen is still isn't fixed
2) the position of isotopes is not shown 
3)He used the basis of placeing as atomic masses  (from lower to higher)due to which some elements with higher atomic mass  are placed before followed by elements with lower atomic masses

 
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Balkaran Singh , added an answer, 1 week, 1 day ago
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Limitations of Mandeleev’s periodic table : Inspite of many advantages, the Mendeleev’s periodic table has certain defects also. Some of these are given below ;

(A) Position of hydrogen : Position of hydrogen in the periodic table is uncertain. It has been placed in 1A group with alkali metals, but certain properties of hydrogen resemble those of halogens. So, it may be placed in the group for halogens as well.

(B) Position of isotopes : Isotopes are the atoms of the same element having different atomic masses. Therefore, according to Mendeleev’s classification these should be placed at different places depending upon their atomic masses. For example, hydrogen isotopes with atomic masses 1,2 and 3 should be placed at three places. However, isotopes have not been given separate places in the periodic table because of their similar properties.

(C) Anomalous pairs of elements “ In certain pair of elements, the increasing order of atomic masses was not obeyed. In these, Mendeleev placed elements according to similarities in their properties and not in increasing order of their atomic masses.

 For example :

– The atomic mass of argon is 39.9 and that of potassium 39.1 But argon is placed before potassium in the periodic table.

– Tellurium (at. mass = 127.6 ) is placed before iodine (at. mass = 126.9)

(D) Some similar elements are separated, in the periodic table. For example copper (Cu) and mercury (Hg), barium (Ba) and lead (Pb). On the other hand some dissimilar elements have been placed together in the same group.

(E) Cause of periodicity : Mendeleev could not explain the cause of periodicity among the elements.

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Muskan , added an answer, 1 week, 5 days ago
105 helpful votes in Science
The limitations of mendeleev are as follows:
  • he cannot tell the position of hydrogen
  • he cannot tell the position of isotopes
  • he cannot tell the position of anomalous pairs.
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Khan Shoeb , added an answer, 6 days ago
4 helpful votes in Science
1.could not explain isotopes of elements
2.could not explain the increasing atomic mass
3.could not assign proper position of hydrogen in its table
 
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Tanishq , added an answer, 3 days, 4 hours ago
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was unable to determine the position of hydrogen and position of isotopes 
 
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Simran Jaiswal , added an answer, on 17/2/17
1 helpful votes in Science
The position of isotopes. Position of hydrogen. Positionof Ni & Co.
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Vijay , added an answer, 1 week, 1 day ago
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thanks thats nice information.
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Subhasree Nayak , added an answer, on 26/6/14
84 helpful votes in Science

Limitations of Mendeleevs periodic table:

  • The position of hydrogen is not justified in Mendeleevs periodic table. He positioned it in the first column above alkali metals. He did so because hydrogen and alkali metals have similar electronic configurations. Also, hydrogen reacts with halogens, oxygen and sulphur to form compounds whose formulae are similar to those of alkali metals.

Table: Hydrogen and alkali metals reacting with halogens

However, like halogens, hydrogen too is a gas and exists as a diatomic molecule (H2). It forms covalent compounds like halogens, and unlike alkali metals. Hence, it can also be placed above the halogen group.

Hence, we can say that hydrogen resembles alkali metals as well as halogens, and can be placed above either of them. This means that hydrogen cannot have a fixed position in the periodic table. Therefore, it is a limitation of Mendeleevs periodic table that hydrogen is not assigned a correct position in it.

  • The discovery of isotopes revealed another limitation of Mendeleevs periodic table. Atoms of the same elements having different number of neutrons are called isotopes. Isotopes have the same number of protons and electrons, but different number of neutrons. For example, the isotopes of chlorine are Cl-35 and Cl-37. They have the same chemical properties, but different atomic masses. Since Mendeleevs periodic table is based on the atomic masses of elements, isotopes have to be placed in different columns despite the fact that they represent the same element.

  • In Mendeleevs periodic table, atomic masses do not increase in a regular manner. As a result, it is not possible to predict the number of elements that might be present between two elements.

  • Although Mendeleev arranged the elements in the increasing order of their atomic masses, there are instances where he has placed an element with a slightly higher atomic mass before an element with a slightly lower atomic mass. For example, cobalt (whose atomic mass is 58.9) is placed before nickel (whose atomic mass is 58.7). This reversal was done to maintain a consistency in the properties of the elements present in a column, i.e., to group the elements with similar properties together.

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Varsha Rimjhim , added an answer, 3 days ago
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there is no fixed position of hydrogen.
dissimilar elements are placed together 
 
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Prajwal Nayak , added an answer, 4 days, 3 hours ago
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bosudike
 
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Rudra , added an answer, 3 days, 23 hours ago
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I have my ans in my text book come to my home i will tell u
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Ankita , added an answer, on 25/1/17
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position of hydrogen and isotopes are not defined .
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Vishal Toshniwal , added an answer, on 29/1/15
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1 Position of isotopes
2 Position of Hydrogen
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Subhasree Nayak , added an answer, on 14/4/15
84 helpful votes in Science
the position of hydrogen was not correctly defined.it was placed in group 1 although it resembles both the group 1 element.the alkali metals and the group 7 elements the halogens in thier properties.
in some cases mendeleev placed some elements according to thier similarties properties not by thier increasing order of thier atomic masses.thus the position of these elements was not justified.
isotopes were not given separate places in the peroidic table.
some similar elements were group separately while some dissimilar elements were grouped together.
mendeleev could not explain the cause of peroidicity in the elements.
the position of lathenide and actinide were not included in this table.
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Subhasree Nayak , added an answer, on 14/4/15
84 helpful votes in Science
the position of hydrogen was not correctly defined.it was placed in group 1 although it resembles both the group 1 element.the alkali metals and the group 7 elements the halogens in thier properties.
in some cases mendeleev placed some elements according to thier similarties properties not by thier increasing order of thier atomic masses.thus the position of these elements was not justified.
isotopes were not given separate places in the peroidic table.
some similar elements were group separately while some dissimilar elements were grouped together.
mendeleev could not explain the cause of peroidicity in the elements.
the position of lathenide and actinide were not included in this table.
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Vijay Vannam , added an answer, on 15/12/16
5 unhelpful votes in Science
1 Position of hydrogen 2 Anomalous pair of element 3 Dissimilar elements placed together 4 Some similar element are separated 5 Position of Isotope
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Arnav Kaul , added an answer, on 5/2/17
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it will help u
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Bhanu Chhonkar , added an answer, on 7/8/13
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haan

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Noraiz Rana , added an answer, on 10/1/13
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 position of lanthanide tell  ma about this

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Arnav Kaul , added an answer, on 5/2/17
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refer to ncert
 
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Rohit Verma , added an answer, on 23/12/16
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Limitations are
1. Position of hydrogrn was not defined
2. Position of lanthinides and anthanides is not defined
3. Position of transation triades
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Ijas , added an answer, on 7/12/13
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Refer 10th Science Text book Page No.84. - LIMITATIONS OF MENDELEEV' S CLASSIFICATIONS

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