Right the Lewis structures for the following three molecules and ions, including the dots for external electron’s and lines for single double and triple bonds. 1. BH2- 2. N2H2 3. CNH3
The Correct Answer and Explanation is:
Correct Lewis Structures:
- BH₂⁻ (Borohydride Ion):
cssCopyEdit H–B:⁻–H
Explanation: Boron (B) has 3 valence electrons. Each hydrogen contributes 1, and the negative charge adds 1 extra electron, giving a total of 6 electrons. Boron forms two single bonds with hydrogen atoms, and one lone pair (shown as a colon) due to the extra electron. The structure is bent with one lone pair on B.
- N₂H₂ (Diazene or Diimide):
mathematicaCopyEdit H–N=N–H
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Explanation: Each nitrogen atom has 5 valence electrons, and each hydrogen has 1. The structure has a double bond between the two nitrogen atoms to fulfill the octet rule, and each nitrogen is also bonded to one hydrogen atom. Each nitrogen also retains one lone pair. The molecule is planar with sp² hybridization at each nitrogen.
- CNH₃ (Aminocyanide or a resonance structure of methyl isocyanide):
mathematicaCopyEdit H–N–C≡N
Explanation: This structure assumes a linear backbone. The carbon forms a triple bond with nitrogen (C≡N), and a single bond with nitrogen (N). The nitrogen bonded to H is tetrahedral with a lone pair and three single bonds to hydrogen atoms. The central carbon has 4 valence electrons, bonding with nitrogen in a triple bond and the other nitrogen in a single bond. The terminal nitrogen in the triple bond has a lone pair.
300-Word Explanation (without “we”):
Lewis structures illustrate how atoms share or transfer electrons to achieve stability in a molecule or ion. In BH₂⁻, boron starts with three valence electrons and forms two single bonds with hydrogen atoms. The negative charge indicates one extra electron, which results in a lone pair on the boron atom. The total of six valence electrons is distributed among bonds and the lone pair.
In N₂H₂, each nitrogen atom brings five valence electrons, while each hydrogen contributes one. A double bond between the nitrogen atoms enables both to fulfill the octet rule. Each nitrogen also forms a single bond with a hydrogen atom. One lone pair remains on each nitrogen, and the structure assumes a planar geometry due to sp² hybridization.
The CNH₃ molecule includes a central carbon atom bonded to a nitrogen atom and a cyano group. The triple bond between carbon and nitrogen (C≡N) satisfies the octet rule for both atoms. The nitrogen bonded to carbon (–NH₃) forms three single bonds with hydrogen atoms and contains one lone pair. The arrangement allows for proper distribution of electrons across the atoms. Each atom reaches a stable electron configuration by forming covalent bonds and retaining necessary lone pairs.
Correct Lewis structures provide insight into molecular shape, reactivity, and polarity. Bond types (single, double, triple) influence electron distribution and molecular geometry. Electron pairs not involved in bonding are represented as dots (lone pairs), which affect shape and reactivity. Understanding these structures is fundamental to predicting behavior in chemical reactions.
