Which of the following best describes a key structural difference between ionic and covalent compounds?

• A. Ionic compounds form a lattice of alternating positive and negative ions, while covalent compounds consist of discrete molecules held together by shared electron pairs.
• B. Ionic compounds contain only nonmetals, while covalent compounds contain only metals.
• C. Ionic compounds have low melting points, while covalent compounds have high melting points.
• D. Ionic compounds are always gases at room temperature, while covalent compounds are always solids.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the nature of ionic compounds. Ionic compounds are formed by the electrostatic attraction between positively charged cations and negatively charged anions. These ions arrange themselves in a repeating three-dimensional pattern called a lattice.
2. Step 2: Understand the nature of covalent compounds. Covalent compounds consist of atoms that share pairs of electrons to form discrete molecules. These molecules are held together by covalent bonds, which involve shared electron pairs between atoms.
3. Step 3: Compare the structural differences. Ionic compounds form extended lattice structures with alternating positive and negative ions, resulting in a solid network. Covalent compounds, on the other hand, form individual molecules that are separate entities.
4. Step 4: Evaluate the other options. Ionic compounds do not contain only nonmetals; they typically form between metals and nonmetals. Also, ionic compounds generally have high melting points due to strong ionic bonds, while covalent compounds can have varying melting points. Additionally, ionic compounds are usually solids at room temperature, not gases.
5. Step 5: Conclude that the key structural difference is that ionic compounds form a lattice of alternating ions, whereas covalent compounds consist of discrete molecules held together by shared electron pairs.