Which one of the following substances crystallizes as a covalent crystal?
CaO
SiO2
CO2
Pb
KMnO4
SiO2
Both SiO2 and CO2 are covalent.
Among the substances given, SiO2 (silicon dioxide) is the one that crystallizes as a covalent crystal.
To determine which substance crystallizes as a covalent crystal, we need to understand what covalent crystals are and examine the chemical properties of each substance.
Covalent crystals are formed when atoms are held together by covalent bonds, which involve the sharing of electrons between atoms. In these crystals, the atoms are tightly bonded to each other in a large three-dimensional network, creating a solid structure with a repeating pattern.
Let's analyze the given substances:
1. CaO (calcium oxide) - Calcium oxide is an ionic compound and does not form covalent crystals. It consists of positively charged calcium ions (Ca2+) and negatively charged oxide ions (O2-).
2. SiO2 (silicon dioxide) - Silicon dioxide, also known as quartz, is a prime example of a covalent crystal. It forms a network structure in which each silicon atom is bonded to four oxygen atoms by covalent bonds.
3. CO2 (carbon dioxide) - Carbon dioxide is a molecular compound with covalent bonds between carbon and oxygen atoms. However, it does not form a covalent crystal because its individual molecules do not link together in a long-range periodic arrangement.
4. Pb (lead) - Lead is a metallic element and does not form covalent crystals. It exhibits metallic bonding, where the atoms are held together by a "sea" of delocalized electrons.
5. KMnO4 (potassium permanganate) - Potassium permanganate is an ionic compound composed of potassium (K+) and permanganate (MnO4-) ions. It does not form covalent crystals.
Based on the analysis, SiO2 (silicon dioxide) is the substance that crystallizes as a covalent crystal.