Atomic Foundations of Matter | Class 9 Science Notes

Naming Covalent and Ionic Compounds

Naming covalent compounds involves using prefixes to indicate the number of atoms of each element in the molecule. The first element retains its name, while the second element ends with -ide. Prefixes such as mono-, di-, tri-, tetra-, penta-, hexa- indicate the number of atoms, with some pronunciation rules to avoid awkward sounds. For example, CO is carbon monoxide, CO2 is carbon dioxide, and SF6 is sulfur hexafluoride. When hydrogen is the first element, no prefix is used regardless of the number of hydrogen atoms, e.g., H2S is hydrogen sulfide. Some compounds have common names like water (H2O) and ammonia (NH3). Naming ionic compounds involves writing the cation name first followed by the anion name ending in -ide for simple ions. Polyatomic ions have specific names and do not end with -ide. The names and valencies of common monoatomic and polyatomic ions are tabulated. This systematic naming helps in clear communication and understanding of chemical substances.

📊 Diagram: Table on page 13 (20×3) listing common monoatomic ions with formulas and valencies; Table on page 14 (7×3) listing common polyatomic ions with formulas and valencies.

🔗 Connection: This section leads to writing chemical formulae of covalent and ionic compounds.

Table on page 13 (20×3)

Table on page 14 (7×3)

Table on page 21 (5×4)