a In the modern Periodic Table why does cobalt with higher atomic mass of 5893 appear before nickel ...

Question

a In the modern Periodic Table why does cobalt with higher atomic mass of 5893 appear before nickel having lower atomic mass of 5871 b Why could no fixed position be given to hydrogen in Mendeleevs periodic table

Accepted Answer

a In the modern periodic table elements are arranged according to the increasing atomic number The atomic number of cobalt and nickel is 27 and 28 respectively Therefore cobalt has a higher atomic mass and appears before nickel in the periodic table b Mendeleevs period law failed to explain the position of hydrogen as it resembles both the properties of group 1 alkali metals and group 17 halogens Hydrogen reacts with the metal to form ionic compounds called hydrides and also with nonmetals to form covalent compounds

Lakhmir Singh Solutions Class 10 Chemistry Solutions for Exercise in Chapter 5 - Chapter 5 Periodic Classification of Elements