Final answer:
An ammonia (NH₃) molecule is formed when a nitrogen atom shares one of its valence electrons with each of the three hydrogen atoms, resulting in the formation of three single covalent bonds to complete both nitrogen's and hydrogens' valence shells.
Step-by-step explanation:
The statement that best explains how an ammonia (NH₃) molecule is formed with covalent bonds is: Nitrogen shares one of its valence electrons with each hydrogen atom. A neutral nitrogen atom has five valence electrons and falls into group 15. According to its Lewis electron structure, the nitrogen atom in ammonia has one lone pair and shares three bonding pairs with hydrogen atoms, thus forming three single covalent bonds.
Each hydrogen atom needs one more electron to complete its valence shell, and the nitrogen atom needs three more electrons to complete its valence shell. Therefore, three pairs of electrons must be shared amongst the four atoms involved. This sharing of electrons is the defining characteristic of a covalent bond, and in this case, results in the formation of an ammonia molecule.
Group 15 elements like nitrogen form three covalent bonds to achieve a stable octet, as illustrated in the Lewis structure of ammonia where the nitrogen atom is bonded to three hydrogen atoms, coinciding with its three unpaired electrons.