Every chemical element undergoes a reaction in order to fulfill the completion of their outermost shell. This is the case of nitrogen (symbol "N"), which is an element found in group 5 of the periodic table with atomic number 7 (i.e. 1s2 2s2 2p3). It possesses three valence electrons in it's outermost shell.
Looking at the configuration of the Nitrogen atom, it requires three electrons to complete its electron shell. Hence, nitrogen will enter a reaction in order to have its need for THREE ELECTRONS met in order to have its electron shell full.
Note that, nitrogen enters a chemical reaction to look for three electrons not three neutrons.
Electronic configuration represents the total number of electrons that a neutral element contains. We add all the superscripts to know the number of electrons in an atom. The electrons are filled according to Afbau's rule in order of increasing energies.
The last electron enters the third shell in all elements from Sodium to Argon.
A rock is a natural occuring no living thing that has a definite structure from the physical characteristics Marcie saw in the rock she picked it tends to rock because unlike minerals rocks has definite structure.