Question

Predict whether each of the following compounds is molecular or ionic: (a) \(\mathrm{B}_{2} \mathrm{H}_{6}\), (b) \(\mathrm{CH}_{3} \mathrm{OH}\), (c) \(\mathrm{LiNO}_{3}\) (d) \(\mathrm{Sc}_{2} \mathrm{O}_{3}\), (e) \(\mathrm{CsBr}_{\text {, }}(\mathrm{f}) \mathrm{NOCl}\), (g) \(\mathrm{NF}_{3}\), (h) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\).

Short answer

(a) \(\mathrm{B}_{2} \mathrm{H}_{6}\): molecular, (b) \(\mathrm{CH}_{3} \mathrm{OH}\): molecular, (c) \(\mathrm{LiNO}_{3}\): ionic, (d) \(\mathrm{Sc}_{2} \mathrm{O}_{3}\): ionic, (e) \(\mathrm{CsBr}\): ionic, (f) \(\mathrm{NOCl}\): molecular, (g) \(\mathrm{NF}_{3}\): molecular, (h) \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\): ionic.

Step-by-step solution

(1) Classify \(\mathrm{B}_{2} \mathrm{H}_{6}\)

Boron (B) and Hydrogen (H) are both nonmetals. As a result, \(\mathrm{B}_{2} \mathrm{H}_{6}\) is held together by covalent bonds and is therefore considered a molecular compound.

(2) Classify \(\mathrm{CH}_{3} \mathrm{OH}\)

Carbon (C), Hydrogen (H), and Oxygen (O) are all nonmetals. Hence, \(\mathrm{CH}_{3} \mathrm{OH}\) is held together by covalent bonds and is considered a molecular compound.

(3) Classify \(\mathrm{LiNO}_{3}\)

Lithium (Li) is a metal, while Nitrogen (N) and Oxygen (O) are nonmetals. Since this compound contains a metal and nonmetal, ionic bonds are formed, making \(\mathrm{LiNO}_{3}\) an ionic compound.

(4) Classify \(\mathrm{Sc}_{2} \mathrm{O}_{3}\)

Scandium (Sc) is a metal, and Oxygen (O) is a nonmetal. The compound \(\mathrm{Sc}_{2} \mathrm{O}_{3}\) is held together by ionic bonds due to the interaction between a metal and a nonmetal, so it is an ionic compound.

(5) Classify \(\mathrm{CsBr}\)

Cesium (Cs) is a metal, and Bromine (Br) is a nonmetal. The interaction between metal and nonmetal forms ionic bonds in this compound, making \(\mathrm{CsBr}\) an ionic compound.

(6) Classify \(\mathrm{NOCl}\)

Nitrogen (N), Oxygen (O), and Chlorine (Cl) are all nonmetals. Thus, \(\mathrm{NOCl}\) has covalent bonds and is classified as a molecular compound.

(7) Classify \(\mathrm{NF}_{3}\)

Nitrogen (N) and Fluorine (F) are both nonmetals, so \(\mathrm{NF}_{3}\) is held together by covalent bonds, making it a molecular compound.

(8) Classify \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\)

Silver (Ag) is a metal, while Sulfur (S) and Oxygen (O) are nonmetals. The interaction between metal and nonmetal results in ionic bonds. Therefore, \(\mathrm{Ag}_{2} \mathrm{SO}_{4}\) is an ionic compound.

Key concepts

Chemical Bonding

Chemical bonding is the process that holds atoms together in compounds. Atoms form bonds to achieve a more stable electron configuration. There are mainly two types of chemical bonds: covalent and ionic.

Covalent bonds occur when atoms share one or more pairs of electrons, leading to the formation of a molecule. This type of bond typically forms between nonmetal atoms. Conversely, ionic bonds result from the transfer of electrons from one atom to another, creating ions that attract each other due to opposite charges – usually between metal and nonmetal atoms.

The type of bond directly influences the properties of the resulting compound, such as melting and boiling points, solubility, and electrical conductivity. Grasping the differences between these bonds is fundamental for predicting the behavior of compounds in various chemical reactions and environments.

Classification of Compounds

Compounds can be broadly classified into two categories: molecular (or covalent) compounds and ionic compounds. This classification is based on the type of chemical bonds that hold the atoms together in a compound.

Molecular Compounds

Molecular compounds are composed of molecules formed by covalent bonds. They typically consist of nonmetal elements. These compounds have distinct features such as lower melting and boiling points, and they tend not to conduct electricity when dissolved in water because they do not produce ions.

Ionic Compounds

On the other hand, ionic compounds are formed by ionic bonds between metal cations and nonmetal anions. They usually have high melting and boiling points, and they can conduct electricity in the molten state or when dissolved because they form ions in solution. Identifying the type of compound is critical in predicting and explaining its physical and chemical properties.

Covalent Bonds

Covalent bonds are a type of chemical bond where electron pairs are shared between atoms. These bonds form between nonmetal atoms with similar electronegativities – a measure of an atom's tendency to attract electrons.

In a covalent bond, the shared electrons occupy the outer shell of both atoms, leading to a stable electronic structure. Molecules with covalent bonds exhibit a diverse range of physical properties depending on whether they are formed from polar or nonpolar covalent bonds.

• Polar covalent bonds: Unequal sharing of electrons due to different electronegativities of the bonding atoms.
• Nonpolar covalent bonds: Equal sharing of electrons, as the electronegativities are similar.

By understanding the type of covalent bond, one can predict molecular properties such as polarity, interaction with other molecules, and solubility in different solvents.

Ionic Bonds

Ionic bonds are formed when electrons are transferred completely from one atom to another, resulting in the formation of charged ions. These ions, with opposite charges, attract each other and form a solid lattice structure.

This kind of bonding typically occurs between metals, which have a propensity to lose electrons and form positively charged cations, and nonmetals, which tend to gain electrons and form negatively charged anions. The resulting ionic compounds are held together by the strong electrostatic forces between the ions.

Ionic compounds have characteristic high melting and boiling points, making them solid at room temperature. Additionally, when dissolved in water or melted, they become conductive because the ions are free to move, which allows them to carry an electric current. Ionic compounds are also generally soluble in polar solvents like water but insoluble in nonpolar solvents.