Free Science Lessons: Understanding Chemical Formulas

Introduction

• Goal: Interpret a chemical formula.
• Challenge: Students may find it tricky initially but can grasp the concept over time.

Key Concepts

• Chemical Formula: Represents the elements in a molecule and the number of atoms of each element.
• Periodic Table: Displays all different elements, each with a symbol (starts with a capital letter, and may have a second lowercase letter).

Examples of Chemical Formulas

Hydrogen Fluoride

• Formula Analysis:
  • Elements: Hydrogen (H) and Fluorine (F)
  • Number of Atoms:
    • Hydrogen: 1 (no number denotes one atom)
    • Fluorine: 1 (no number denotes one atom)

Potassium Iodide

• Formula Analysis:
  • Elements: Potassium (K) and Iodine (I)
  • Number of Atoms:
    • Potassium: 1
    • Iodine: 1

Calcium Sulfate

• Formula Analysis:
  • Elements: Calcium (Ca), Sulfur (S), and Oxygen (O)
  • Number of Atoms:
    • Calcium: 1
    • Sulfur: 1
    • Oxygen: 4 (denoted by the small number 4 next to O)
• Key Idea: The number of atoms of each element in a compound is fixed.
  • Example: Calcium Sulfate (CaSO₄) vs Calcium Sulfite (CaSO₃) - changing a small number alters the compound.

Magnesium Hydroxide

• Formula Analysis:
  • Elements: Magnesium (Mg), Oxygen (O), and Hydrogen (H)
  • Number of Atoms:
    • Magnesium: 1 (no number means one atom)
    • Oxygen: 2
    • Hydrogen: 2
• Brackets in Formulas: Brackets indicate multiplication of the number inside by the number outside.
  • Example: Brackets containing O and H with a small 2 outside results in 2 atoms of each.

Practice Problems

• First Compound:

  • Elements: Copper (Cu) and Iodine (I)
  • Number of Atoms: 1 of each

• Second Compound:

  • Elements: Iron (Fe) and Bromine (Br)
  • Number of Atoms: 1 Iron, 2 Bromine

• Third Compound:

  • Elements: Zinc (Zn), Carbon (C), and Oxygen (O)
  • Number of Atoms: 1 Zinc, 1 Carbon, 3 Oxygen

• Fourth Compound:

  • Elements: Aluminum (Al), Oxygen (O), and Hydrogen (H)
  • Number of Atoms: 1 Aluminum, 3 Oxygen, 3 Hydrogen

Additional Resources

• For further practice, refer to the myvision workbook available through the provided link.

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