Question

Which one of the following molecules contains both ionic and covalent bonds? (a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\) (b) \(\mathrm{K}_{2} \mathrm{SO}_{4}\) (c) \(\mathrm{BeCl}_{2}\) (d) \(\mathrm{SO}_{2}\)

Short answer

The molecule is (b) \(\mathrm{K}_{2} \mathrm{SO}_{4}\). It contains both ionic and covalent bonds.

Step-by-step solution

Identify Compounds with Covalent Bonds

Covalent bonds are generally found in molecules where atoms share electrons. These are typically seen in nonmetal-to-nonmetal bonds. - **Analysis**: In (a) \(\mathrm{CH}_{2} \mathrm{Cl}_{2}\), (c) \(\mathrm{BeCl}_2\), and (d) \(\mathrm{SO}_2\), the atoms are nonmetals or include \(\mathrm{Be}\) which can form coordinate covalent bonds.

Identify Compounds with Ionic Bonds

Ionic bonds result from the electrostatic attraction between oppositely charged ions, which often occur between metals and nonmetals.- **Analysis**: (b) \(\mathrm{K}_{2} \mathrm{SO}_{4}\) includes \(\mathrm{K}\) (a metal) and \(\mathrm{SO}_{4}^{2-}\) (a polyatomic ion). This composition signifies the presence of ionic bonds between \(\mathrm{K}^{+}\) ions and \(\mathrm{SO}_{4}^{2-}\) ions.

Determine Polyatomic Ions in the Molecules

Polyatomic ions such as \(\mathrm{SO}_{4}^{2-}\) in \(\mathrm{K}_{2} \mathrm{SO}_{4}\) consist of covalently bonded atoms. This means within the ion \(\mathrm{SO}_{4}\), the sulfur and oxygen atoms are connected by covalent bonds.

Conclusion of Both Bond Types

Since \(\mathrm{K}_{2} \mathrm{SO}_{4}\) combines ionic bonds between \(\mathrm{K}\) and \(\mathrm{SO}_{4}\) and covalent within \(\mathrm{SO}_{4}\),it exhibits both bond types in contrast with other options.

Key concepts

Ionic Bonds

Ionic bonds occur when there is a full transfer of electrons from one atom to another, creating charged particles known as ions. This bond is typically formed between metals and nonmetals, which have significantly different electronegativities. For example, in the compound \( \mathrm{K}_{2} \mathrm{SO}_{4} \), potassium (K) donates an electron to become \( \mathrm{K}^{+} \), and the sulfate ion (\( \mathrm{SO}_{4}^{2-} \)) accepts these electrons. The potassium ions are positively charged while the sulfate ion is negatively charged, and the electrostatic attraction between these charged ions holds the compound together. Ionic bonds often result in the formation of a crystalline lattice structure and create compounds with high melting and boiling points.

Covalent Bonds

Covalent bonds are characterized by the sharing of electron pairs between atoms. This type of bonding is common in molecules composed of nonmetals. Unlike ionic bonds, where electrons are transferred, in covalent bonds electrons are shared, allowing each atom to attain a stable electronic configuration similar to noble gases. For instance, in the \( \mathrm{SO}_{4}^{2-} \) ion present in \( \mathrm{K}_{2} \mathrm{SO}_{4} \), sulfur shares electrons with oxygen to form covalent bonds. This sharing of electrons enables the entire ion to have an overall negative charge. Covalent bonds can be single, double, or triple, depending on how many pairs of electrons are shared between the atoms, affecting the molecule's strength and stability.

Polyatomic Ions

Polyatomic ions are ions that consist of two or more atoms covalently bonded together, and which function as a single charged entity. An example of a polyatomic ion is sulfate \( \mathrm{SO}_{4}^{2-} \), found in \( \mathrm{K}_{2} \mathrm{SO}_{4} \). Within the ion, sulfur and oxygen atoms share electrons creating covalent bonds, yet the entire group maintains an overall charge. Polyatomic ions can exhibit multiple bonding scenarios: they can accept, donate, or share electrons with other ions, creating compounds that combine both covalent and ionic characteristics. These ions are crucial in explaining the dual bonding nature in compounds such as \( \mathrm{K}_{2} \mathrm{SO}_{4} \), where both ionic and covalent bonds exist.

Molecular Structure

The molecular structure of a compound is determined by the arrangement of atoms and how they are bonded together. Understanding the structure helps explain the physical and chemical properties of the molecule. In compounds like \( \mathrm{K}_{2} \mathrm{SO}_{4} \), the molecular structure is influenced by both ionic and covalent bonds. The potassium ions form ionic bonds with the sulfate ion, while within the sulfate ion itself, the sulfur and oxygen atoms are covalently bonded. This combination affects properties such as solubility, conductivity, and reactivity. For instance, the molecular structure can influence whether a compound dissolves in water or if it conducts electricity. Thus, deciphering the molecular structure is essential to predict how a compound will behave in various conditions.