Q9 of 60 Page 1

The electrons in the atoms of four elements A, B, C and D are distributed in three shells having 1, 3, 5 and 7 electrons in the outermost shell respectively. State the period in which these elements can be placed in the modem periodic table. Write the electronic configuration of the atoms of A and D and the molecular formula of the compound formed when A and D combine.

Since the electrons in the atoms of four elements A, B, C and D are distributed in three shells which are having 1, 3, 5 and 7 electrons in the outermost shell. So, the electronic configuration of elements A, B, C and D is as follows:


A: 2, 8, 1


B: 2, 8, 3


C: 2, 8, 5


D: 2, 8, 7


Since all the elements have three sub-shells, so they belong to 3rd period.


We need to find the valency of element A and D, to find the molecular formula of the compound


Since, element A has 1 valence electron, therefore valency of A is 1. Also, Element D has 7 valence electrons, so valency of D is 1.


Cross multiplying the valences of element A and element D:



Therefore, the compound formed is: AD


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Study the following table in which positions of six elements A, B, C, D, E arid F are shown as they are in the modem periodic table:


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(i) Name the element which forms only covalent compounds.


(ii) Name the element which is a metal with valency three.


(iii) Name the element which is a non-metal with valency three.


(iv) Out of D and E, which is bigger in size and why?


(v) Write the common name for the family to which the elements C and F belong.

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