Ch.10 - Chemical Bonding I: The Lewis Model

Problem 86

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Chapter 10, Problem 86

Which of the two compounds, H₂NNH₂ and HNNH, has the strongest nitrogen-nitrogen bond, and which has the shorter nitrogen-nitrogen bond.

Verified step by step guidance

Step 1: Identify the type of bonds in each compound. In H2NNH2, the nitrogen atoms are connected by a single bond. In HNNH, the nitrogen atoms are connected by a triple bond.

Step 2: Understand the relationship between bond strength and bond length. Generally, the stronger the bond, the shorter the bond length. This is because stronger bonds pull the atoms closer together.

Step 3: Apply this understanding to the compounds in question. The triple bond in HNNH is stronger than the single bond in H2NNH2, so HNNH has the stronger nitrogen-nitrogen bond.

Step 4: Similarly, because the bond in HNNH is stronger, it is also shorter. Therefore, HNNH has the shorter nitrogen-nitrogen bond.

Step 5: In conclusion, HNNH has both the stronger and the shorter nitrogen-nitrogen bond compared to H2NNH2.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Covalent Bonding

Covalent bonding occurs when two atoms share electrons to achieve a full outer shell, leading to the formation of molecules. The strength of a covalent bond is influenced by factors such as the number of shared electron pairs and the electronegativity of the atoms involved. In the case of nitrogen-nitrogen bonds, the presence of lone pairs and the overall molecular structure can significantly affect bond strength.

Bond Length

Bond length is the distance between the nuclei of two bonded atoms. It is influenced by the size of the atoms and the type of bond formed. Generally, shorter bonds are stronger due to the increased overlap of atomic orbitals, which leads to a more stable interaction. In nitrogen compounds, variations in hybridization and steric effects can alter bond lengths.

Resonance Structures

Resonance structures are different ways of drawing a molecule that can represent the same arrangement of atoms but differ in the distribution of electrons. These structures help explain the delocalization of electrons in molecules, which can affect bond strength and length. In compounds like H2NNH2 and HNNH, resonance can influence the nitrogen-nitrogen bond characteristics, leading to variations in stability and bond properties.

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Resonance Structures

Related Practice

Write Lewis structures for each molecule or ion. Use expanded octets as necessary. b. AsF₆^-

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Textbook Question

Order these compounds in order of increasing carbon–carbon bond strength: HCCH, H₂CCH₂, H₃CCH₃.

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Textbook Question

Order these compounds in order of decreasing carbon–carbon bond length: HCCH, H₂CCH₂, H₃CCH₃.

Hydrogenation reactions are used to add hydrogen across double bonds in hydrocarbons and other organic compounds. Use average bond energies to calculate ΔH_rxn for the hydrogenation reaction. H₂C=CH₂(g) + H₂(g) → H₃C–CH₃(g)

Ethanol is a possible fuel. Use average bond energies to calculate ΔHrxn for the combustion of ethanol. CH₃CH₂OH(g) + 3 O2(g) → 2 CO₂(g) + 3 H₂O(g)

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Textbook Question

Ethane burns in air to form carbon dixode and water vapor.

2 H3C¬CH3( g) + 7 O2( g)¡4 CO2( g) + 6 H2O( g)

Use average bond energies to calculate ΔHrxn for the reaction.