Answer
There are 2 core electrons, 5 valence electrons and 3 unpaired electrons in nitrogen.
Work Step by Step
Nitrogen has 7 electrons The electron configuration of nitrogen is $$N: 1s^22s^22p^3$$
The nearest noble gas element of lower atomic number is $He$, which has the electron configuration $1s^2$. Therefore, the condensed electron configuration of nitrogen is $$N: [He]2s^22p^3$$
1) Looking here, we see that there are 2 inner-shell electrons (those that occupy the first shell) and 5 outer-shell electrons (those that occupy the second shell). Also, since nitrogen has the atomic number less than 30, all outer-shell electrons are valence electrons.
Therefore, there are 2 core electrons and 5 valence electrons.
2) The unpaired electrons are those who does not have the accompanying electrons which have the opposite electron spin in an orbital.
We see from the electron configuration of nitrogen that all the s-orbitals have been fully occupied (the upper number is 2).
The maximum number of electrons that a p subshell can have are 6 (p subshell has 3 orbitals, each orbital can carry 2 electrons at most). Here, only 3 electrons are present. According to Hund's rule, to achieve the most stable situation, each of these 3 electrons will occupy a separate orbital that a p subshell has.
That means 3 orbitals here each carries only 1 electron. Therefore, there are 3 unpaired electrons in nitrogen.
