Writing Formulas and Naming Binary Compounds

Chemical Compounds

  • Binary Compounds:

    • Composed of two elements.

    • Broadly classified into:

      • Ionic Compounds (metal + nonmetal)

      • Covalent Compounds (two nonmetals)

Ionic Compounds

  • Definition: Composed of ions (charged atoms or groups).

  • Formation:

    • Made from metals and nonmetals.

    • Smallest unit known as formula unit, representing the smallest neutral unit of an ionic compound.

Properties of Ionic Compounds

  • High melting points.

  • Conduct electricity when:

    • Melted or dissolved in water.

  • Electrically neutral (sum of charges on ions equals zero).

Types of Ionic Compounds

  • Type I: Metal forms only one cation.

  • Type II: Metal can form multiple cations with different charges.

Writing Ionic Formulas

  • Steps:

    1. Write cation symbol followed by anion symbol.

    2. Ensure the total charge is zero.

Rules for Writing Ionic Formulas

  1. Cation first in formula.

  2. Subscripts should produce a neutral formula unit.

  3. Use smallest whole number subscripts.

  4. Omit charges from final formula.

Determining Ionic Formulas

  • Example: Magnesium and Oxygen

    • Magnesium forms +2 ion; Oxygen forms -2 ion; thus, MgO.

  • Criss-Cross Rule: Use the charge of one ion as the subscript for the other to find the formula.

Naming Chemical Compounds

  • Type I Ionic Compounds: Name the cation, then the anion with -ide.

  • Type II Ionic Compounds: Use Roman numerals to indicate the charge of the cation.

Type III Binaries (Covalent Compounds)

  • Formed between two nonmetals.

  • Use prefixes for number of atoms.

  • The prefix mono- is never used for the first element.

Common Polyatomic Ions

  • Examples:

    • Ammonium (NH4+)

    • Nitrate (NO3-)

    • Sulfate (SO4^2-)

Naming Ionic Compounds with Polyatomic Ions

  • Similar to binary compounds but polyatomic ions are expressed in parentheses when needed.

Exercise Questions**

  • Practice naming and writing formulas based on the rules.

  • Example: KClO3 is potassium chlorate.

Hydrates

  • Ionic compounds with water of crystallization.

  • Named by the ionic compound followed by the number of water molecules using Greek prefixes.

Conclusion

  • Understanding the types, properties, and naming conventions helps in comprehending chemical compounds.