Q9 of 24 Page 5

Consider element "A" (17)and "B"(19)Find the position and write the electron dot structure.(CBSE 2014, 2013)

The electron configuration of elements are as follows:

Be – 2, 2


Ca – 2, 8, 8, 2


Mg – 2, 8, 2


4Be, 12Mg, 20Ca


(a) Since all the elements have same no. of valence electrons i.e. 2, so they all belongs to group 2.


(b) Since there are only 2 shells in Be due to which the forces of attraction between nucleus and its electrons is strong due to which it can’t lose electrons easily. Therefore, it is the least reactive.


(c) As Ca has maximum shells and therefore it will have largest atomic size.

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The electronic configuration of four elements A, B, C and D is given as follows:

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