Final answer:
The molecule NH3 (ammonia) has a Lewis dot structure with only one unshared pair of valence electrons, which is the lone pair on the nitrogen atom. In contrast, H2O2 (hydrogen peroxide) has two lone pairs, so it does not meet the criteria.
Step-by-step explanation:
The Lewis dot structure of NH3 (ammonia) shows only one unshared pair of valence electrons. In this molecule, the central nitrogen atom has a total of five valence electrons. It forms three covalent bonds with hydrogen atoms by sharing three of its valence electrons. The remaining two valence electrons on the nitrogen constitute one lone pair, resulting in one unshared pair of electrons in the Lewis structure.
In contrast, the molecule H2O2 (hydrogen peroxide) has an oxygen atom with six valence electrons, forming a total of two covalent bonds and leaving two lone pairs, or two unshared pairs of electrons. Therefore, H2O2 does not meet the criteria of having only one unshared pair of valence electrons.
Lewis structures visually represent the arrangement of electrons in molecules. They show bonding pairs of electrons usually with a line and nonbonding lone pairs as dots. For NH3, it would be represented with three lines indicating bonds with hydrogen atoms and a pair of dots representing the lone pair on nitrogen.