Identifying Covalent Compounds

Understanding the type of chemical bond in a compound helps us classify it as ionic or covalent. Ionic compounds typically form between metals and non-metals, involving the transfer of electrons. Covalent compounds usually form between two non-metals or metalloids, involving the sharing of electrons.

Analyzing the Options for Chemical Bonding

Let's examine each given option to determine its bonding type:

• Calcium oxide (CaO): Calcium (Ca) is a metal, and Oxygen (O) is a non-metal. Compounds formed between metals and non-metals are generally ionic due to a large difference in electronegativity. Calcium oxide is a classic example of an ionic compound.
• Sodium nitride (Na₃N): Sodium (Na) is an alkali metal, and Nitrogen (N) is a non-metal. Similar to calcium oxide, compounds formed between alkali metals and non-metals are strongly ionic. Sodium nitride is an ionic compound.
• Silicon carbide (SiC): Silicon (Si) is a metalloid (often behaving chemically like a non-metal) and Carbon (C) is a non-metal. Compounds formed between two non-metals or a metalloid and a non-metal typically exhibit covalent bonding. Silicon and carbon share electrons to form strong covalent bonds, often resulting in network covalent structures.
• Zinc sulphide (ZnS): Zinc (Zn) is a metal, and Sulphur (S) is a non-metal. While compounds between metals and non-metals are often ionic, some can have significant covalent character, especially when the electronegativity difference is not very large, or the metal is a transition metal. Zinc sulphide has bonding that can be described as having substantial covalent character within an ionic lattice structure. However, compared to silicon carbide (formed purely between metalloid/non-metal and non-metal), silicon carbide is a more clear example of a predominantly covalent compound in this list.

Comparison Based on Electronegativity Difference

We can also look at the electronegativity difference ($\Delta \text{EN}$) between the elements involved. A larger difference generally indicates more ionic character, while a smaller difference suggests more covalent character. Using Pauling electronegativity values:

Based on electronegativity differences, Silicon carbide ($\Delta \text{EN} = 0.65$) clearly falls into the covalent range ($\Delta \text{EN} < 1.7$), especially compared to the other options which have much larger differences indicating significant ionic character.

Conclusion

Considering the nature of the elements involved and the electronegativity differences, Silicon carbide (SiC) is the covalent compound among the given options. Calcium oxide and Sodium nitride are ionic compounds. Zinc sulphide exhibits some covalent character but is often considered to have more ionic or polar covalent bonding compared to the strongly covalent nature of SiC.

Revision Table: Compound Types

Additional Information on Covalent Bonding

Covalent bonds form when atoms share electrons to achieve a stable electron configuration, typically a full valence shell (octet rule). The sharing occurs between non-metal atoms because they have similar electronegativities and neither atom is strong enough to completely pull electrons away from the other. Covalent compounds can exist as discrete molecules (like water, H₂O, or carbon dioxide, CO₂) or as large network solids where atoms are linked by a continuous network of covalent bonds (like diamond, graphite, or silicon carbide). Network covalent solids are typically very hard, have high melting points, and are poor conductors of electricity.