Question

Modern periodic table is arranged in order of increasing mass numbers :

• A. True
• B. False

Answer 1

The correct option is B False

1) Modern periodic table is arranged in order of increasing atomic numbers and after filling of 7 elements in the second period after lithium the eighth element sodium has same property as that of the lithium and hence placed just below lithium.Same type of periodicity is seen in other periods also. Therefore according to the similarity in the properties they are arranged in the periodic table.
2) The periodic repetition of the elements with similar properties after certain regular interval when atoms arearranged in increasing order of atomic number is called periodicity. The periodic repetition of the properties is due to the recurrence of the similar valence shell configuration after certain regular interval.
The properties of the elements exhibit trends or periodicity. These trends can be predicted using the periodic table and can be explained and understood by analyzing the electron configurations of the elements. Elements tend to gain or lose valence electrons to achieve stable octet formation.
The periodic repetition of the properties of the elements is due to the recurrence of similar valence shellelectronic configurations after certain regular intervals. For example, alkalimetals have same valence shellelectronic configuration $n{s}^1$, therefore, have similar properties.