Question

Which of the following substances exhibit hydrogen bonding interactions? a. \(\mathrm{CCl}_{2} \mathrm{H}_{2}\) b. \(\mathrm{BeF}_{2}\) c. \(\mathrm{NO}_{3}^{-}\) d. HCN

Short answer

Based on the analysis, only HCN (option d) exhibits hydrogen bonding interactions, as it contains a hydrogen atom bonded to a highly electronegative nitrogen atom.

Step-by-step solution

Analyze Substance a - \(\mathrm{CCl}_{2}\mathrm{H}_{2}\)

In this molecule, there are two hydrogen atoms bonded to two carbon atoms. Since carbon is not a highly electronegative atom (like oxygen, nitrogen, or fluorine), hydrogen bonding interactions cannot occur in this substance.

Analyze Substance b - \(\mathrm{BeF}_{2}\)

Beryllium fluoride is an ionic compound composed of beryllium and fluorine atoms. There are no hydrogen atoms in this compound, so hydrogen bonding interactions are not possible.

Analyze Substance c - \(\mathrm{NO}_{3}^{-}\)

Nitrate ion (\(\mathrm{NO}_{3}^{-}\)) consists of a central nitrogen atom surrounded by three oxygen atoms. Although oxygen is a highly electronegative atom, there are no hydrogen atoms present in this ion. Therefore, hydrogen bonding interactions cannot occur.

Analyze Substance d - HCN

In hydrogen cyanide (HCN), there is a hydrogen atom bonded to a nitrogen atom. Nitrogen is highly electronegative, and this interaction allows for hydrogen bonding with another electronegative atom.

Conclusion

Based on our analysis, only HCN (option d) exhibits hydrogen bonding interactions.

Key concepts

Chemical Bonding

Chemical bonding is at the heart of understanding molecular interactions and the structure of substances. It refers to the attractive force that holds atoms together in compounds. There are three primary types of chemical bonds: ionic, covalent, and metallic. Ionic bonding occurs when electrons are transferred from one atom to another, leading to the formation of positively and negatively charged ions. Covalent bonding involves the sharing of electron pairs between atoms, and it's the type of bond that allows hydrogen bonding interactions to occur within certain molecules.

In the context of the exercise, hydrogen bonding is a unique type of interaction that can be considered a strong form of a covalent bond. It arises when a hydrogen atom, covalently bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine, experiences attraction to another electronegative atom in a different molecule. Understanding the nature of the atoms involved in a substance, and how they are bonded, is crucial to determining whether hydrogen bonding is possible, as highlighted in the solution to the exercise for HCN.

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons within a chemical bond. The scale of electronegativity ranges from 0 to 4, with fluorine being the most electronegative element at 4.0. Electronegativity plays a pivotal role in determining the type and strength of chemical bonds. Elements with high electronegativity, such as nitrogen, oxygen, and fluorine, are more likely to form covalent bonds and participate in hydrogen bonding.

The significance of electronegativity in relation to the exercise lies in its ability to indicate whether hydrogen bonding interactions are likely. For instance, in HCN, the nitrogen atom has a high electronegativity, enabling the molecule to engage in hydrogen bonding with other molecules. This concept helps elucidate why HCN, unlike the other substances listed, exhibits hydrogen bonding interactions.

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion that act between neighboring particles (atoms, molecules, or ions). These forces are largely responsible for various physical properties of compounds, such as boiling points, melting points, and solubility. Among the different types of intermolecular forces, hydrogen bonding is often discussed due to its significance in affecting the physical properties of substances.

Hydrogen Bonding stands out as one of the strongest types of intermolecular forces and occurs specifically between molecules that have hydrogen atoms covalently bonded to highly electronegative elements. The exercise successfully shows that only HCN has the suitable condition for hydrogen bonding – a hydrogen atom bonded to a highly electronegative atom (nitrogen in this case). This is why HCN has higher boiling and melting points compared to other molecules of similar size that do not have hydrogen bonds.