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(7) F(9) P(15) Ar(18)

Answer 1

Hint: The atomic number of an element is equal to the number of electrons present in that atom.
The elements which are chemically similar mean they contain the same number of valence electrons in the shell.

Complete step by step solution:
(a) We have to find the atomic number of the element corresponding to the electronic configuration 2, 8, 7.
-The atomic number of an element is nothing but the total number of electrons present in it.
-So, the number of electrons present in an atom = 2+8+7 = 17.
-Therefore the atomic number of the element is equal to 17.
(b)
-The element having atomic number 17 is Chlorine.
-The electronic configuration of chlorine is \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{5}}\].
-The valence electrons in chlorine are 7.
-We have to find the chemically similar element to chlorine.
-The given elements are Nitrogen (7), Fluorine (9), Phosphorous (15), Argon (18).
-To know about the valence electrons present in Nitrogen (7), Fluorine (9), Phosphorous (15), and Argon (18). We should know the electronic configuration of those elements.
-Electronic configuration of Nitrogen (7) = \[1{{s}^{2}}2{{s}^{2}}2{{p}^{3}}\]
-Electronic configuration of Fluorine (9) = \[1{{s}^{2}}2{{s}^{2}}2{{p}^{5}}\]
-Electronic configuration of Phosphorus (15) = \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{3}}\]
-Electronic configuration of Argon (18) = \[1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{6}}\]
-Therefore the elements Nitrogen, phosphorus and argon have valence electrons 5, 5 and 8 respectively.
-But Fluorine has 7 valence electrons.
-Chlorine and fluorine both have similar electronic configuration and the same number of valence electrons.
-So, the chemical element which is chemically similar to chlorine is fluorine.

Note: In the periodic table the elements present in the groups have the same electronic configuration and the same number of valence electrons. So, all the elements present in the same group have the same chemical properties.