CBSE Class 10 Science 2017 · Paper 531 · Question 9
The electronic configuration of an element is 2, 8, 7.
- (i)What is the group number and period number of this element in the Modern Periodic Table ?
- (ii)Is this element a metal or a non-metal ? Give reason to justify your answer.
Answer
Period 3, group 17 (chlorine); it is a non-metal because it gains one electron to complete its octet.
(i) The electrons occupy three shells, so the element is in period 3; it has 7 valence electrons, so it is in group 17 (). It is chlorine, atomic number .
(ii) It is a non-metal. With 7 electrons in its outermost shell it needs only one more to complete its octet, so it tends to gain one electron and form a negative ion (2, 8, 8); gaining electrons is the behaviour of non-metals. Its position in group 17, on the right-hand side of the table, agrees.
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