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

Answer 1

Answer:

a) periods indicate the number of shells so the elements having one shell are placed in first period and those which have two shells are present in second period. same is the case with elements in third, forth, fifth, sixth and seventh period.

b) most of the chemical properties depend upon number of electrons in outermost shell. however, elements in same group have same number of electrons in their outermost shells.

d) Groups indicate the number of electrons in outermost shell. however, chlorine and florine both have 7 electrons in their outermost shells thats why they are placed in 7 A group