question_answer 23)

Compare and contrast the arrangement of elements in Mendeleev's periodic table and the modern periodic table. 

Answer:

(i) In Mendeleef's periodic table the elements are arranged in the increasing order of masses. On the other hand, in the modem periodic table the elements are arranged increasing order of atomic numbers which is more fundamental property than atomic   (ii) In the Mendeleef periodic table, the position of the elements was in accordance with mass. In the modern periodic table the position of the elements is governed by electronic configurations, which determine their properties.   (iii) In Mendeleef periodic table, the position of isotopes was not justified. In Modem  periodic table, the classification is based on the atomic number and not atomic mass and hence the position of isotopes is fully justified.   (iv) Mendeleef periodic table had some anomalies on the basis of atomic mass. In modern periodic law, there are no misfits in terms of atomic number. For example, in Mendeleef's periodic table, potassium was having position lower than argon. But in Modern periodic table, this has been solved. Argon precedes potassium because argon has atomic number 18 and potassium has 19.   (v) The Mendeleef periodic table does not explain satisfactorily as to why the properties of the elements are repeated at regular intervals of 2, 8, 18 and 32. The modern periodic table explain this logically.   (vi) There is no clear cut separation of different types of elements in the Mendeleef’s periodic table. In modern periodic table there is clear cut separation of different types of elements such as representative elements, noble gases, transition elements. (vii) Mendeleef periodic table is not easy to remember. Modern periodic table is easy to remember.