CLASS – X, BOSEM
Chapter – 3 PERIODIC CLASSIFICATION OF ELEMENTS
1. State and explain Mendeleev’s Periodic law. Write the characteristics of the Mendeleev’s
Periodic Table.
Ans: Statement: The properties of elements are the periodic functions of their atomic masses.
Explanation: When the elements are arranged in order of increasing atomic masses then
those with similar properties are repeated at regular intervals.
Characteristics of the periodic table : Its main characteristics are :
(i) The periodic table consists of eight vertical columns called groups and six horizontal rows
called periods.
(ii) The eight groups are designated as I, II, III, IV, V, VI, VII and VIII. Except group VIII, each
group is divided into two sub-groups as A and B. Elements of left side group A constitute
normal or representative elements while elements of right side group B constitute
transition elements.
(iii) The horizontal rows or periods are numbered 1, 2, 3, 4, 5 and 6. In order to accomodate
more elements, the periods 4, 5, 6 are divided into two halves. The first half ofthe elements
are placed in the upper left corners and the second half occupy lower right corners in each
box.
2. Write the achievements and limitations of the Mendeleev’s Periodic Table.
Ans: Achievements:
(i) Study of the elements:
The periodic table made the study of the elements easier. Knowing the properties of one
element in a group, the properties of other elements in the group can be easily guessed.
(ii) Prediction of new elements and their properties :
While arranging the elements in order of their atomic masses, Mendeleev left some vacant
places in the table and boldly predicted the existence and properties of some undiscovered
elements. For example, scandium, gallium and germanium, discovered later, have properties
similar to eka-boron, eka-aluminium and eka-silicon respectively predicted by Mendeleev.
Chapter – 3 PERIODIC CLASSIFICATION OF ELEMENTS
1. State and explain Mendeleev’s Periodic law. Write the characteristics of the Mendeleev’s
Periodic Table.
Ans: Statement: The properties of elements are the periodic functions of their atomic masses.
Explanation: When the elements are arranged in order of increasing atomic masses then
those with similar properties are repeated at regular intervals.
Characteristics of the periodic table : Its main characteristics are :
(i) The periodic table consists of eight vertical columns called groups and six horizontal rows
called periods.
(ii) The eight groups are designated as I, II, III, IV, V, VI, VII and VIII. Except group VIII, each
group is divided into two sub-groups as A and B. Elements of left side group A constitute
normal or representative elements while elements of right side group B constitute
transition elements.
(iii) The horizontal rows or periods are numbered 1, 2, 3, 4, 5 and 6. In order to accomodate
more elements, the periods 4, 5, 6 are divided into two halves. The first half ofthe elements
are placed in the upper left corners and the second half occupy lower right corners in each
box.
2. Write the achievements and limitations of the Mendeleev’s Periodic Table.
Ans: Achievements:
(i) Study of the elements:
The periodic table made the study of the elements easier. Knowing the properties of one
element in a group, the properties of other elements in the group can be easily guessed.
(ii) Prediction of new elements and their properties :
While arranging the elements in order of their atomic masses, Mendeleev left some vacant
places in the table and boldly predicted the existence and properties of some undiscovered
elements. For example, scandium, gallium and germanium, discovered later, have properties
similar to eka-boron, eka-aluminium and eka-silicon respectively predicted by Mendeleev.
