U3 Aleks Binary Ionic Compounds

Deriving the Formula of Binary Ionic Compounds

Definition and Overview

  • Binary Ionic Compound: A compound composed of two different elements, where each element forms a single atomic ion.
  • The goal is to derive the formula based on the name of the compound.

Example 1: Strontium Chloride

  • Start with the compound name: Strontium Chloride.

    • Identify the Cation (Positively Charged Ion):
    • Cation: Strontium (Sr)
    • Locate Strontium on the periodic table: Symbol = Sr
    • Common Charge of Strontium: Group 2, thus charge = +2
      • Write:
      • Strontium Charge: +2
    • Identify the Anion (Negatively Charged Ion):
    • Anion: Chloride
    • First syllable from Chlorine (Cl) + suffix -ide means it is derived from chlorine.
    • Common Charge of Chloride: Always -1
      • Write:
      • Chloride Charge: -1
      • Symbol = Cl

  • Charge Neutrality:

    • Strontium ion has a charge of +2 and chloride ion has a charge of -1.
    • To achieve charge neutrality (total charge = 0), require two chloride ions to balance the +2 charge from strontium:
    • Write: Cl with subscript 2 → Cl₂

  • Final Formula: Combine the symbols while ensuring charge neutrality:

    • Strontium Chloride formula: SrCl₂

Example 2: Sodium Oxide

  • Start with the compound name: Sodium Oxide.

    • Identify the Cation (Positively Charged Ion):
    • Cation: Sodium (Na)
    • Locate Sodium on the periodic table: Symbol = Na
    • Common Charge of Sodium: Group 1, thus charge = +1
      • Write:
      • Sodium Charge: +1
    • Identify the Anion (Negatively Charged Ion):
    • Anion: Oxide
    • First syllable from Oxygen (O) + suffix -ide means it is derived from oxygen.
    • Common Charge of Oxide: Always -2
      • Write:
      • Oxide Charge: -2
      • Symbol = O

  • Charge Neutrality:

    • Sodium ion has a charge of +1 and oxide ion has a charge of -2.
    • To achieve charge neutrality, need two sodium ions to balance the -2 charge from oxide:
    • Write: Na with subscript 2 → Na₂

  • Final Formula: Combine the symbols while ensuring charge neutrality:

    • Sodium Oxide formula: Na₂O

Summary of Steps for Naming Binary Ionic Compounds

  1. Identify the cation and anion from the name of the compound.
  2. Determine the charge of each ion based on its position in the periodic table.
  3. Ensure charge neutrality by adjusting the subscripts of the ions appropriately.
  4. Write the correct formula as a combination of the cation and anion symbols, adjusting for total charge balance.