Chapter 5 Part B: Molecules and Compounds

Learning Objectives

• Understand molecular or covalent compounds.
• Define molecular or covalent compounds.
• Learn how to write and name molecular compounds.

Molecular (Covalent) Compounds

Definition

• Covalent Bonds:
  • Formed when atoms share electrons to achieve a stable electron configuration.
  • Typically involve nonmetals from groups 4A, 5A, 6A, 7A, and hydrogen from group 1A.

Examples

• Chlorine Molecule (Cl₂):

  • Chlorine shares one electron with another chlorine atom, forming a single covalent bond, depicted with a single line.
  • Each chlorine attains a stable electron count similar to Argon.

• Oxygen Molecule (O₂):

  • Oxygen atoms share two electron pairs, resulting in a double bond (depicted with two lines).
  • Both oxygens achieve a stable electron configuration similar to Neon.

• Nitrogen Molecule (N₂):

  • Nitrogen atoms share three electron pairs, forming a triple bond.
  • Each nitrogen atom achieves a stable configuration like Neon.

Writing and Naming Molecular Compounds

Writing Molecular Formulas

• Write the element farther from fluorine first.
• Example: PCl₅ (Phosphorus pentachloride)
  • Phosphorus (farther from fluorine) is written first, then chlorine.
  • Subscripts indicate the number of atoms (5 chlorines).

Naming Molecular Compounds

• First element retains its name.
• Second element is modified to end in "-ide".
• Use prefixes to indicate the number of atoms:
  • Mono (1), Di (2), Tri (3), Tetra (4), Penta (5), Hexa (6), etc.
• Examples:
  • Phosphorus Pentachloride
  • Dichlorine Monoxide / Dichlorine Oxide
  • Dinitrogen Tetroxide

Exercise Examples

• NO₂: Nitrogen dioxide
• PCl₃: Phosphorus trichloride
• ICl₃: Iodine trichloride

Identifying Compound Types

• Covalent Compounds:
  • Composed of nonmetals.
  • Example: SO₂ (Sulfur dioxide)
• Ionic Compounds:
  • Involve metals and nonmetals.
  • Example: BaCl₂ (Barium chloride), Ca₃(PO₄)₂ (Calcium phosphate)
  • Transition metals require charge notation, e.g., Cu₂CO₃ (Copper(I) carbonate)

Conclusion

• Reviewed definition and examples of molecular compounds.
• Discussed writing and naming rules in detail.
• Preview for next session: Chapter 5 Part C on acids and formula mass.