Problem 67 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following represents the Lewis structure of \(\mathrm{N}_{2}\) molecule? (a) \({ }_{x}^{x} \mathrm{~N} \equiv \mathrm{N}_{x}^{\mathrm{x}}\) (b) \({ }_{\mathrm{x}}^{\mathrm{x}} \mathrm{N} \equiv \mathrm{N}_{\mathrm{x}}^{\mathrm{x}}\) (c) \({ }_{\mathrm{x}}^{\mathrm{x}} \mathrm{N}_{x \mathrm{x}} \equiv \mathrm{N}_{\mathrm{x}}^{\mathrm{xx}} \mathrm{x}^{\mathrm{x}}\) (d) \({ }_{x}^{x}{\underline{\phantom{xx}}}_{x}^{x x}-\underset{x x}{N}-\stackrel{x x}{x}\)

Step-by-Step Solution

Answer

(a) and (b) are correct; both show a triple bond and lone pairs.

Step 1: Understanding the Nitrogen Atom

A nitrogen atom represents atomic number 7, meaning it has 5 valence electrons. When determining the Lewis structure, we aim to fulfill the octet rule, which dictates that atoms tend to combine in such a way that each atom has eight electrons in its valence shell.

Step 2: Understanding the Triple Bond in N2

Since nitrogen has 5 valence electrons, two nitrogen atoms will need to share three pairs of electrons (total six electrons) to fulfill the octet rule for both atoms. This sharing forms a triple bond, one of the strongest types of bonds, commonly represented as \( \equiv \).

Step 3: Determining the Correct Representation

The Lewis structure for each nitrogen atom in \( \mathrm{N}_{2} \) should show five valence electrons: three shared in the triple bond and one lone pair on each nitrogen. Option (a) \({}_x^x N \equiv N{}_x^x\) accurately depicts this structure with the triple bond and lone pairs.

Step 4: Elimination of Incorrect Options

Option (b) is identical to (a) but written slightly differently. Option (c) includes extra elements that are incorrect for \( \mathrm{N}_2 \). Option (d) incorrectly depicts a single bond and other symbols irrelevant to the \( \mathrm{N}_2 \) molecule. Hence only (a) or (b) can be correct.

Key Concepts

Understanding The Octet Rule

The octet rule is a fundamental concept in chemistry that helps predict the bonding behavior of atoms. It states that atoms tend to form bonds in such a way that each atom has eight electrons in its valence shell, achieving a stable electron configuration similar to the noble gases. This drive to fulfill or mimic a complete set of eight electrons is the basis of many chemical reactions and bonding scenarios.
In the case of nitrogen \(\mathrm{N}_2\), each nitrogen atom starts with five valence electrons. To satisfy the octet rule, both nitrogen atoms need extra electrons to reach a total of eight valence electrons each. This is achieved through bonding, specifically by sharing electrons between atoms.

• A molecule will strive to achieve an electron configuration that satisfies this rule.
• Atoms will often share electrons as a means to fulfill the octet requirement, resulting in covalent bonds.
• In nitrogen's case, mutual sharing of electrons results in a strong triple bond that effectively provides each nitrogen atom with access to eight electrons.

Following the octet rule enables chemists to predict the number and types of bonds that can form between atoms.

Unraveling The Triple Bond

A triple bond is a type of chemical bond where three pairs of electrons are shared between two atoms. This type of bond is represented by three lines or equals signs \( \equiv \), and it is one of the strongest and shortest types of covalent bonds. In the nitrogen molecule \(\mathrm{N}_2\), the triple bond is a crucial feature that significantly influences the molecule's properties.
When two nitrogen atoms combine, each contributes three electrons to the bond, resulting in six electrons shared between them. This satisfies the octet rule for both nitrogen atoms, as they effectively "see" eight electrons in their respective outer shells.

• Triple bonds are stronger than both single and double bonds, which involve fewer shared electron pairs.
• They also make the molecule more chemically stable and less reactive under standard conditions.
• The triple bond in \(\mathrm{N}_2\) gives it unique characteristics, such as being colorless and odorless, and largely inert, requiring significant energy to break the bond.

Understanding the strength and structure of a triple bond is vital when studying molecular stability and reactivity.

The Importance Of Valence Electrons

Valence electrons are the outermost electrons of an atom and are pivotal in determining how that atom will bond and interact with others. For nitrogen, which is in group 15 of the periodic table, there are five valence electrons.
These electrons play a critical role in chemical bonding because they are the electrons that participate in bond formation. Atoms will share, lose, or gain valence electrons to satisfy the octet rule, forming various types of bonds including covalent, ionic, and metallic bonds.

• Valence electrons define the electron configuration and behavior of elements.
• They are responsible for forming bonds and thus determine the molecule's structure.
• In molecules like nitrogen \(\mathrm{N}_2\), understanding the number of valence electrons is key to predicting the bonding pattern.

Mastering the concept of valence electrons is essential for understanding chemical reactions, Lewis structures, and the behavior of molecules in different environments.