Problem 41 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The hydrogen bond is strongest in : (a) \(\mathrm{O}-\mathrm{H} \ldots \ldots \ldots \mathrm{S}\) (b) \(\mathrm{S}-\mathrm{H} \ldots \ldots \ldots \mathrm{O}\) (c) \(\mathrm{F}-\mathrm{H} \ldots \ldots \ldots \mathrm{F}\) (d) \(\mathrm{F}-\mathrm{H}, \ldots \ldots \ldots \mathrm{O}\)

Step-by-Step Solution

Answer

The strongest hydrogen bond is in option (c) \(\mathrm{F}-\mathrm{H} \ldots \mathrm{F}\).

Step 1: Understanding Hydrogen Bonding

Hydrogen bonding is a type of attractive interaction that occurs between a hydrogen atom bonded to a highly electronegative atom (like F, O, or N) and another electronegative atom. This bond is strongest when the electronegativity difference between the involved atoms is highest.

Step 2: Analyzing Each Option

Let's examine each option:(a) \(\mathrm{O}-\mathrm{H} \ldots \mathrm{S}\): Oxygen is more electronegative than sulfur.(b) \(\mathrm{S}-\mathrm{H} \ldots \mathrm{O}\): Oxygen is more electronegative than sulfur; however, SH bond usually does not form strong hydrogen bonds.(c) \(\mathrm{F}-\mathrm{H} \ldots \mathrm{F}\): Fluorine is the most electronegative element.(d) \(\mathrm{F}-\mathrm{H} \ldots \mathrm{O}\): Both fluorine and oxygen are highly electronegative.

Step 3: Determining Electronegativity Impact

The strength of a hydrogen bond is greatly influenced by the electronegativity of the participating atoms. Fluorine has the highest electronegativity of all the elements, making \( \mathrm{F}-\mathrm{H} \) bonds notably strong in hydrogen bonding contexts.

Step 4: Conclusion Based on Electronegativity

Considering electronegativity, option (c) \(\mathrm{F}-\mathrm{H} \ldots \mathrm{F}\) features hydrogen bonds between fluorine atoms, which is the strongest due to fluorine's position at the top of the electronegativity scale.

Key Concepts

Electronegativity

Electronegativity is a key concept in chemistry that describes an atom's ability to attract and bind with electrons. It plays a crucial role in determining how atoms interact with one another, especially in the formation of bonds. In the periodic table, electronegativity typically increases from left to right across a period and decreases down a group.

Some important points to note about electronegativity include:

• Fluorine has the highest electronegativity on the periodic table, with a value of 3.98 on the Pauling scale.
• Atoms with higher electronegativity values indicate a stronger tendency to seize electrons when forming chemical bonds.
• Electronegativity differences between atoms can predict bond types: nonpolar covalent (small difference), polar covalent (moderate difference), and ionic (large difference).

Understanding these electronegativity differences is pivotal as it dictates not only the bond strength but also the bond's character, which can be decisive when evaluating interactions like hydrogen bonding.

Chemical Bonds

Chemical bonds are the forces that hold atoms together in molecules and compounds. These bonds enable the atoms to achieve stability through the sharing or transferring of electrons. Three primary types of chemical bonds exist:

• Covalent Bonds: Involves the sharing of electron pairs between atoms. These can be polar (unequal sharing due to differences in electronegativity) or nonpolar (equal sharing).
• Ionic Bonds: Formed when one atom donates an electron to another, leading to positive and negative ions that attract each other. This bond typically occurs between metals and nonmetals.
• Metallic Bonds: In these bonds, electrons are shared loosely among a lattice of metal atoms, allowing for conductivity and malleability.

Hydrogen bonds, a special type of dipole-dipole attraction, though not a true "bond," are crucial because they influence the physical properties of compounds, such as boiling and melting points. Their strength is often dependent on electronegativity differences, making certain atom combinations like F-H particularly strong. This is due to fluorine's high electronegativity.

Fluorine

Fluorine is a highly reactive, pale yellow gas at room temperature, known for being the most electronegative element on the periodic table. This characteristic makes fluorine incredibly important in the study of chemical bonding and interactions.

Key attributes of fluorine:

• Atomic number 9, symbol F, and part of the halogen group (Group 17/VIIA).
• Its high electronegativity and small atomic radius allow it to pull electrons towards itself very effectively.
• Fluorine often forms strong covalent bonds with hydrogen, shown in compounds like hydrogen fluoride (HF). These bonds significantly contribute to the strength of hydrogen bonds.

Fluorine's presence in a F-H-F bond setup results in extremely strong hydrogen bonds, as demonstrated in the given solution where F-H-F has the strongest hydrogen bond due to fluorine’s ability to attract electrons, making it a formidable participant in such interactions.