Question

The total number of electrons in a nitrogen atom and a chlorine atom are 7 and 17 respectively. Find the number of valence electrons in them.
A) 3,1
B) 5,8
C) 4,1
D) 5,7

Answer 1

As we know, the valence electrons are those electrons that are usually present in the outermost shell of the orbital during the electronic configuration. There are four main orbitals for the electronic configuration.

Complete answer:
We know that, the atomic number of nitrogen is 7 and the electronic configuration of nitrogen is 2,5 which means 2 electrons are present in ${\rm{s}}$ orbital and 5 electrons are present in ${\rm{p}}$ orbital. The five electrons are present in the outermost shell. So, the valence electrons of the nitrogen atom is 5.
Similarly, the atomic number of chlorine is 17 and the electronic configuration of chlorine is 2,8,7 which generally means 2 electrons are present in ${\rm{s}}$ orbital, 8 electrons are present in ${\rm{ s\; and\; p }}$ orbital of second shell and 7 electrons are present in ${\rm{s\; and\; p}}$ orbital of third shell. The seven electrons are present in the outermost shell of chlorine. So, the valence electrons of the chlorine atom is 7.
Thus, the number of valence electrons in nitrogen and chlorine is 5,7 respectively.

Hence, the correct option is D that is 5,7.

Note: The outermost electrons which are usually associated or connected with the respective atoms are termed as valence electrons. The electronic configuration of the atom is necessary for evaluating the valence electrons of an atom.