(a) State the merits of Mendeleev’s classification of elements
(b) Describe two anomalies of Mendeleev’s periodic classification of elements.
(a) State the merits of Mendeleev’s classification of elements
(b) Describe two anomalies of Mendeleev’s periodic classification of elements.
(a) Merits of Mendeleev’s periodic table: Mendeleev’s periodic table was one of the greatest achievements in the development of chemistry. Some of the important contributions of his periodic table are given below ;
(i) A systematic study of elements: He arranged known elements in order of their increasing atomic masses considering the fact that elements with similar properties should fall in the same vertical column.
(ii) Correction of atomic masses: The Mendeleev's periodic table could predict errors in the atomic masses of certain elements were corrected. For example, atomic mass of beryllium was corrected from 13.5 to 9. Similarly, with the help of this table, atomic masses of indium, gold, platinum etc. were corrected.
(iii) Mendeleev predicted the properties of those missing elements from the known properties of the other elements in the same group. Eka-boron, eka-aluminium and eka-silicon names were given for scandium, gallium and germanium (not discovered at the time of Mendeleev).
(iv) The position of noble gases: Noble gases like helium (He), neon (Ne) and argon (Ar) were mentioned in many studies. However, these gases were discovered very late because they are very inert and are present in extremely low concentrations. One of the achievements of Mendeleev’s periodic table was that when these gases were discovered, they could be placed in a new group without disturbing the existing order.
(b) Anomalous pair
In certain pairs of elements like Ar (40) and K (39); Co (58.9) and Ni (58.6); Te (127.6) and I (126.9) the arrangement was not justified. For e.g., argon was placed before potassium whereas its atomic mass is more than potassium.
(a) Merits of Mendeleev’s periodic table: Mendeleev’s periodic table was one of the greatest achievements in the development of chemistry. Some of the important contributions of his periodic table are given below ;
(i) A systematic study of elements: He arranged known elements in order of their increasing atomic masses considering the fact that elements with similar properties should fall in the same vertical column.
(ii) Correction of atomic masses: The Mendeleev's periodic table could predict errors in the atomic masses of certain elements were corrected. For example, atomic mass of beryllium was corrected from 13.5 to 9. Similarly, with the help of this table, atomic masses of indium, gold, platinum etc. were corrected.
(iii) Mendeleev predicted the properties of those missing elements from the known properties of the other elements in the same group. Eka-boron, eka-aluminium and eka-silicon names were given for scandium, gallium and germanium (not discovered at the time of Mendeleev).
(iv) The position of noble gases: Noble gases like helium (He), neon (Ne) and argon (Ar) were mentioned in many studies. However, these gases were discovered very late because they are very inert and are present in extremely low concentrations. One of the achievements of Mendeleev’s periodic table was that when these gases were discovered, they could be placed in a new group without disturbing the existing order.
(b) Anomalous pair
In certain pairs of elements like Ar (40) and K (39); Co (58.9) and Ni (58.6); Te (127.6) and I (126.9) the arrangement was not justified. For e.g., argon was placed before potassium whereas its atomic mass is more than potassium.
