Question

In which of the following substances, hydrogen bonding is absent? (a) \(\mathrm{H}_{2} \mathrm{O}\) (b) HF (c) Salicylaldehyde (d) \(\mathrm{CCl}_{4}\)

Short answer

Hydrogen bonding is absent in (d) CCl_4.

Step-by-step solution

Understand Hydrogen Bonding

Hydrogen bonding is a special type of dipole-dipole interaction between molecules, which occurs when hydrogen is covalently bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine. This causes a significant dipole, allowing for interactions between molecules.

Analyze Option (a) H_2O

Water (H_2O) has oxygen bonded to hydrogen. Oxygen, being highly electronegative, allows hydrogen bonds to form between water molecules. Therefore, hydrogen bonding is present in H_2O.

Analyze Option (b) HF

Hydrofluoric acid (HF) has fluorine bonded to hydrogen. Fluorine is highly electronegative, which means hydrogen bonding is present in HF.

Analyze Option (c) Salicylaldehyde

Salicylaldehyde contains an -OH group and an -CHO group. The highly electronegative oxygen in the -OH group allows for hydrogen bonding to occur between molecules of salicylaldehyde.

Analyze Option (d) CCl_4

Carbon tetrachloride (CCl_4) is composed of carbon and chlorine atoms. Neither of these atoms is hydrogen bonded directly to a highly electronegative atom necessary for hydrogen bonding. Hence, hydrogen bonding is absent in CCl_4.

Key concepts

Dipole-Dipole Interaction

In chemistry, understanding the way molecules interact is crucial. One important interaction is called dipole-dipole interaction. This occurs between molecules that have permanent dipoles, meaning they have partial positive and negative charges.
For example, if a molecule contains a polar bond, like in hydrogen chloride (HCl), the hydrogen atom becomes slightly positive while the chlorine atom becomes slightly negative. When these molecules come close to each other, the positive end of one molecule is attracted to the negative end of another molecule, this is what we call a dipole-dipole interaction.

• These interactions are stronger than Van der Waals forces but weaker than covalent or ionic bonds.
• They play a significant role in determining the properties of substances, such as boiling and melting points.
• For hydrogen bonding, which is a special type of dipole-dipole interaction, the hydrogen atom must be bonded to highly electronegative atoms like nitrogen, oxygen, or fluorine to create a strong dipole.

Electronegativity

Electronegativity is a fundamental concept that describes how strongly an atom attracts electrons towards itself when forming a chemical bond. The higher the electronegativity, the stronger the pull on the electrons.
In the context of hydrogen bonding, electronegativity is particularly important. Atoms like nitrogen, oxygen, and fluorine are highly electronegative, meaning they draw the bonding electron pair closer and induce a partial negative charge on themselves. Meanwhile, the hydrogen atom becomes partially positive.

• The difference in electronegativity between bonded atoms determines if a bond is polar or nonpolar.
• Electronegativity values can be found on the Pauling scale, which is a numerical representation.
• Understanding electronegativity helps predict molecule shapes, behaviors, and interactions.

Molecule Interaction

Molecule interaction refers to the ways in which different molecules interact with each other. These interactions are essential for maintaining the structure and function of substances in the natural world.
There are several types of molecule interactions, including dipole-dipole interactions, London dispersion forces, and hydrogen bonds. Each type of interaction varies in strength and influence.

• Hydrogen bonds are strong intermolecular forces that can significantly affect the boiling and melting points of compounds.
• In biological systems, molecule interactions are integral for processes like DNA replication and protein synthesis.
• Recognizing these interactions helps scientists understand material properties and biological functions.

Covalent Bonding

Covalent bonding is a key concept in chemistry, where atoms share pairs of electrons to attain stability in their electron configurations. This bond typically occurs between non-metal atoms.
The electrons shared in covalent bonding contribute to each atom fulfilling its outer electron shell, similar to the electron configuration of noble gases, which are stable.

• Covalent bonds can vary in strength: single bonds share one pair of electrons, double bonds share two pairs, and so on.
• These bonds can lead to the formation of molecules like water (H₂O) and methane (CH₄), with specific shapes and properties related to the type of covalent bonds.
• Polar covalent bonds occur when electrons are not shared equally between the atoms due to a difference in electronegativity.

Hydrogen-Rich Compounds

Hydrogen-rich compounds are those that contain a significant amount of hydrogen atoms. These compounds are essential in various chemical processes and biological systems.
Hydrogen is unique because it can form bonds with many elements, displaying properties like those seen in acids, bases, and hydrocarbons.

• Common hydrogen-rich compounds include water (H₂O), ammonia (NH₃), and methane (CH₄).
• The presence of hydrogen impacts the acidity/basicity of solutions, where it can be present as H⁺ ions.
• In organic chemistry, the hydrogen content in hydrocarbons affects their energy content and combustion properties.