Use covalent Lewis structures to explain why the compound that forms between nitrogen and hydrogen has the formula NH₃. Show why NH₂ and NH₄ are not stable.

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10.5 Covalent Bonding: Lewis Structures The Lewis model provides us with a simple and useful model for covalent bonding. In this model, we represent molecular compounds with Lewis structures, which depict neighboring atoms as sharing some (or all) of their valence electrons in order to attain octets (or duets for hydrogen). Single Covalent Bonds To see how covalent bonding is conceived in terms of the Lewis model, consider hydro- gen and oxygen, which have the following Lewis symbols: HO In water, these atoms share their unpaired valence electrons so that each hydrogen atom gets a duet and the oxygen atom gets an octet as represented with this Lewis structure: HỘ:H The shared electrons-those that appear in the space between the two atoms-count toward the octets (or duets) of both of the atoms. A shared pair of electrons is called a bonding pair, whereas a pair that is associated with only one atom-and therefore not involved in bonding-is a lone pair (shown at left). Lone pair electrons are also called nonbonding electrons. We often represent a bonding pair of electrons by a dash to emphasize that it consti- tutes a chemical bond: