Question

Which of the following statement is wrong? [2011] (a) Single \(\mathrm{N}-\mathrm{N}\) bond is weaker than the single \(\mathrm{P}-\mathrm{P}\) bond (b) Nitrogen cannot form \(\mathrm{d} \pi-\mathrm{p} \pi\) bond (c) The stability of hydrides increases from \(\mathrm{NH}_{3}\) to \(\mathrm{BiH}_{3}\) in group 15 of the periodic table. (d) \(\mathrm{N}_{2} \mathrm{O}_{4}\) has two resonance structures.

Short answer

Option (c) is the incorrect statement.

Step-by-step solution

Analyze Statement (a)

The statement claims that a single \( \mathrm{N}-\mathrm{N} \) bond is weaker than a single \( \mathrm{P}-\mathrm{P} \) bond. In reality, the \( \mathrm{N}-\mathrm{N} \) single bond is indeed weaker than the \( \mathrm{P}-\mathrm{P} \) bond due to repulsion forces between the lone pairs of electrons on nitrogen. This statement is correct.

Analyze Statement (b)

Statement (b) says nitrogen cannot form \( \mathrm{d} \pi-\mathrm{p} \pi \) bonds. Nitrogen typically does not utilize its d-orbitals for bonding because its most common oxidation states and bonding do not require access to d-orbitals, thus it cannot form \( \mathrm{d} \pi-\mathrm{p} \pi \) bonds. This statement is also correct.

Analyze Statement (c)

This statement suggests that the stability of hydrides increases from \( \mathrm{NH}_3 \) to \( \mathrm{BiH}_3 \) within Group 15. However, the stability actually decreases down the group due to increased atomic size and weaker bond strength as you move down, making \( \mathrm{BiH}_3 \) the least stable. Therefore, this statement is incorrect.

Analyze Statement (d)

Statement (d) asserts that \( \mathrm{N}_2 \mathrm{O}_4 \) has two resonance structures. \( \mathrm{N}_2 \mathrm{O}_4 \) can indeed exist in two resonance forms as it delocalizes electrons between the nitrogen and oxygen atoms. Hence, this statement is true.

Key concepts

Periodic Table Group 15

Group 15 of the periodic table is commonly known as the nitrogen group or pnictogens. It includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). These elements are known for having five electrons in their outermost shell, which significantly influences their chemical behavior and bonding characteristics.

• Electron Configuration: Elements in Group 15 have a valence shell electron configuration of ns²np³. This configuration leads to a variety of oxidation states but primarily supports the formation of three covalent bonds by sharing three electrons.
• Gradual Changes Down the Group: As you move down the group, there are noticeable changes in chemical properties like metallic character, which increases from nitrogen (a non-metal) to bismuth (a metal).
• Common Properties: The elements exhibit some characteristic properties such as multiple oxidation states, ability to form polyatomic ions, and participation in both covalent and ionic bonding depending on conditions.

Understanding these elements is essential because they play vital roles in biological systems and industrial processes, especially nitrogen which is vital for life.

Hydride Stability

Hydride stability refers to the resistance of a hydrogen compound of an element to decomposition. In Group 15, the stability of hydrides like ammonia (\(NH_3\)) decreases down the group. This trend is contrary to what some might expect and is crucial for understanding the behavior of these hydrides in different environments.

• Stability Trend: Nitrogen hydride, or ammonia, is the most stable hydride in this group. As you move down the group to phosphorus (PH₃), arsenic (AsH₃), antimony (SbH₃), and finally bismuth (BiH₃), the stability decreases. This decline is due to increasing atomic size and reduced overlap between hydrogen's 1s orbital and the outermost shell of the heavier elements.
• Dynamic Causes: The weakening bond becomes less effective in resisting decomposition as the elements grow larger and the bonds grow longer and weaker.

These stability trends are essential to understand when predicting the reactivity of hydrides, especially in chemical reactions and industrial applications.

Nitrogen Bonding Properties

Nitrogen is highly essential in chemistry due to its versatile bonding properties. In its most stable form, diatomic nitrogen (\(N_2\)), it forms one of the strongest known covalent bonds, the triple bond. This strong bond requires substantial energy to break, which explains nitrogen's inertness under most conditions.

• Covalent Bonding: Nitrogen typically forms three covalent bonds in its compounds, completing its octet by sharing its three unpaired electrons in the 2p orbitals.
• Limitation on d-Orbitals: Unlike heavier Group 15 elements, nitrogen does not participate in \(d\)-orbital bonding (\(d\ \pi-p\ \pi\)bonds), since its empty \(d\)orbitals are not available at energies suitable for chemical bonding.
• Significance of Lone Pairs: Nitrogen's lone pairs considerably influence its chemistry, contributing to specific structural arrangements and participating in hydrogen bonding, which stabilizes many nitrogen-containing compounds.

Recognizing these bonding behaviors is key when dealing with nitrogen in any chemical context, from biological molecules to industrial applications.