Problem 44 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which one among the following does not have the hydrogen bond? [1983-1 Mark] (a) phenol (b) liquid \(\mathrm{NH}_{3}\) (c) water (d) liquid \(\mathrm{HCl}\)

Step-by-Step Solution

Answer

Liquid HCl does not have hydrogen bonds.

Step 1: Identify Compounds Capable of Hydrogen Bonding

Hydrogen bonding occurs when hydrogen is bonded to highly electronegative atoms like oxygen, nitrogen, or fluorine, creating a dipole moment. We will examine each compound to see if they meet these criteria.

Step 2: Analyze Phenol

Phenol has an -OH group, where oxygen is highly electronegative. This allows for hydrogen bonding with other molecules, as the hydrogen in the –OH group can form bonds with electronegative sites in other molecules.

Step 3: Analyze Liquid NH₃

Liquid ammonia (\(NH_3\)) has hydrogen bonded directly to nitrogen, a highly electronegative atom. This configuration supports hydrogen bonding between ammonia molecules.

Step 4: Analyze Water

Water has two hydrogens bonded to oxygen. The oxygen atom is electronegative, making water molecules form strong hydrogen bonds among themselves.

Step 5: Analyze Liquid HCl

In liquid \(HCl\), hydrogen is bonded to chlorine. Although chlorine is electronegative, \(HCl\) does not typically form hydrogen bonds because the electronegative difference required is not as strong as that with oxygen, nitrogen, or fluorine.

Step 6: Determine the Exception

Among the given options, \(HCl\) does not form hydrogen bonds effectively compared to the other choices. Phenol, water, and liquid ammonia can all form hydrogen bonds due to their structure, whereas \(HCl\) cannot.

Key Concepts

Electronegativity

Electronegativity is a chemical property that describes the ability of an atom to attract electrons towards itself in a covalent bond. It plays a crucial role in the formation of hydrogen bonds. The higher the electronegativity of an atom, the more strongly it attracts electrons. When atoms like oxygen, nitrogen, or fluorine, which are highly electronegative, bond with hydrogen, they create a polar bond due to the uneven distribution of electron density.
This uneven sharing of electrons results in a partial negative charge on the electronegative atom and a partial positive charge on the hydrogen atom.

• Oxygen, nitrogen, and fluorine are among the most electronegative elements.
• Electronegativity values influence molecular interactions and properties.
• Understanding electronegativity helps predict molecule behavior.

High electronegativity is a driving force behind the occurrence of phenomena such as hydrogen bonding, as it leads to the development of significant dipole moments in molecules.

Dipole Moment

A dipole moment is a measure of the separation of positive and negative charges in a molecule. It is directly related to the electronegativity of atoms within the molecule.
When a highly electronegative atom, such as oxygen, nitrogen, or fluorine, is bonded with hydrogen, the electrons are drawn more closely to the electronegative atom, establishing a dipole. This gives rise to a molecule where one end is slightly negative, and the other end is slightly positive.

• Dipole moments are vector quantities with both magnitude and direction.
• The larger the dipole moment, the more polar the molecule.
• This polarization influences physical properties like solubility and boiling point.

Dipole moments are essential for understanding how molecules interact, particularly in hydrogen bond formation, as these interactions rely on the attraction between the positive and negative charges.

Hydrogen Bond Formation

Hydrogen bond formation occurs as a result of the interaction between a hydrogen atom bonded to an electronegative atom and another electronegative atom. This is a special type of dipole-dipole interaction often found in molecules where hydrogen is directly attached to oxygen, nitrogen, or fluorine.
The strength of a hydrogen bond depends on several factors, including the electronegativity of the atoms involved, the presence of lone pairs, and the distance between interacting species.

• Hydrogen bonds are relatively strong compared to other intermolecular forces.
• They are pivotal in determining the properties of water, such as its high boiling point and surface tension.
• This bonding is crucial in biological systems, for instance, in stabilizing the structure of proteins and nucleic acids like DNA.

Understanding hydrogen bonds is key to grasping how molecules behave and interact in various environments, making it a foundational concept in chemistry and biology.