Question

An atom has electronic configuration $2,8,7$.
(a) What is the atomic number of this element?
(b) To which of the following elements would it be chemically similar?(Atomic numbers are given in parentheses.)?
$N\left(7\right)$ $F\left(9\right)$ $P\left(15\right)$ $Ar\left(18\right)$

Answer 1

(a)The atomic number of element with electronic configuration $2,8,7=17$.

(b)It has $7$ valence electrons, therefore it would be chemically similar to $F\left(9\right)=2,7$.