a Explain why the first period of the modern periodic table has only two elements whereas second per...

Question

a Explain why the first period of the modern periodic table has only two elements whereas second period has eight elements b Why do elements in the same group show similar properties but the elements in different groups show different properties c For each of the following triads name the element with the characteristics specified below d State one reason for keeping fluorine and chlorine in the same group of the periodic table e What are the merits of the modern periodic table of elements

Accepted Answer

a The first period of the modern periodic table has only two elements whereas the second period has eight elements because the first electron can take a maximum of 2 electrons only and in the 2supndsup period the maximum number of electron which can be put in the 2supndsup shell is 8 b Elements in the same group show similar properties but the elements in different groups show different properties because of the difference in electronic configuration cc i F Br ii Li Li d Fluorine and chlorine have been placed in the same group because both of them have 7 valence electrons e Merits 1 It is based on an atomic number of elements 2 Explains the reason behind showing similar and dissimilar properties in the same and different groups 3 Explains periodicity in the properties of elements 4 There are no anomalies in the arrangement of elements

Elements	Least atomic radius	Chemically least reactive
(i) F, Cl, Br	.....	.....
(ii) Li, Na, K	.....	.....

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