. The atomic number of an element is 17. Predict (a) its valency
(b) whether it is a metal or non-metal, (c) its relative size with respect to other members of its group. Justify your answer in each case
Ans. Atomic number of given element= 17
. .Electronic configuration of given element = 2, 8, 7 (a) Valency = 1
Since this element requires one electron to complete its octet (outermost shell).
(b) This element is a non-metal as it gains one electron to complete its outermost shell and elements which gain electrons are non-metals.
(c) This element is the 2nd member of this group. Its size is greater than the 1st member (2, 7) and smaller than the rest of the other members of that group because size of the atom increases on going down in a group as one energy shell is added at every step.