Q24 of 40 Page 5

In the modem periodic table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium ?

The elctronic configuration of calcium having atomic number 20 is 2, 8, 8, 2. Thus, calcium has 2 valence electrons in its outermost shell. Now, that element which has 2 valence electrons will have physical and chemical properties resembling that of calcium.

The electronic configuration of element having atomic number 12 is 2, 8, 2. It has 2 valence electrons just like calcium. So, the element having atomic number 12 will have physical and chemical properties resembling that of calcium.

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22

Write the number of periods and groups in the Modern Periodic Table. How does the metallic character of elements vary on moving (i) from left to right in a period, and (ii) down a group? Give reason to justify your answer.

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Compare and contrast the arrangement of elements in Mendeleev's periodic table and the Modem periodic table.

 25

Name:

(a) three elements that have a single electron in their outermost shells.


(b) two elements that have two electrons in their outermost shells.


(c) three elements with filled outermost shells.

 26

The elements of a period of the periodic table are given in order from left to right with one of its element missing:


a. To which period do these elements belong?


b. One element of this period is missing. Which is the missing element and where should it be placed?


c. Which one of these elements in this period shows the property of catenation?


d. Which one of these elements is least reactive?