Lecture Notes: Covalent Bonds

Overview

• Covalent Bonds: Atoms form covalent bonds by sharing electrons.
• Comparison with Ionic Bonds: Ionic bonds involve the transfer of electrons resulting in oppositely charged ions held together by electrostatic forces.
• Full Outer Shell: Both types of bonds facilitate atoms attaining a full outer shell of electrons.

Formation of Covalent Bonds

• Non-Metal Elements: Covalent bonds typically occur between non-metal elements.
• Example of Chlorine: Two chlorine atoms each need one extra electron to fill their outer shell. They share electrons to achieve full outer shells.

Representations of Covalent Bonds

• Dot and Cross Diagrams:

  • Draw one atom's electrons as dots and the other's as crosses to distinguish ownership.
  • Sometimes, only the outermost shell is drawn; check specifics if full electron shells are required.

• Displayed Formula:

  • Uses chemical symbols and lines to represent shared electrons.
  • Simplifies drawing of large molecules, such as glucose.
  • Limitation: Does not indicate 3D shape of molecules.

• 3D Models:

  • Illustrate the actual arrangement of atoms.
  • Recognizing 3D models is required, predicting shapes is not yet necessary.

Example: Ammonia (NH₃)

• Molecular Composition: One nitrogen atom and three hydrogen atoms.
• Electron Sharing:
  • Hydrogen needs one extra electron (first energy level holds max two electrons).
  • Nitrogen needs three extra electrons (second energy level holds max eight electrons).
  • Each hydrogen shares one electron with nitrogen, forming full outer shells.

Types of Covalent Substances

• Simple Molecular Substances:

  • Small molecules with strong covalent bonds and weak intermolecular forces.
  • Examples: Chlorine (Cl₂), Ammonia (NH₃), Water (H₂O), Methane (CH₄).

• Polymers and Giant Covalent Structures:

  • Polymers: Long chains with repeating monomer units; used for plastic bags, t-shirts.
  • Giant Covalent Structures:
    • Include silicon dioxide, diamond, and graphite.
    • Features strong covalent bonds and regular lattice structures involving numerous atoms.

Conclusion

• Summary: Covalent bonds are essential for forming various substances by electron sharing.
• Next Steps: Further exploration of polymers and giant covalent structures in other videos.
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