Molecular Shapes and Structure

Introduction to Molecular Shape

• Molecules are mostly empty space.
• Mass is concentrated in the nuclei of atoms.
• Electrons are like clouds of negative charge, not discrete particles.
• Molecules do not have a rigid shape like solid objects.

Factors Influencing Shape

• Arrangement of nuclei and electrons maximizes attraction of opposite charges and minimizes repulsion of like charges.
• Outer electrons primarily determine molecular shape.
• Electron clouds between atoms (bonds) resemble sausages.
• Nuclei are positively charged; electrons are negatively charged.

Historical Discovery

• Alessandro Volta discovered methane in 1776.
• Methane (CH₄) is composed of one carbon and four hydrogen atoms.

Understanding Methane's Structure

• Carbon bonds with up to four atoms; hydrogen bonds with one.
• Carbon is central, bonded to hydrogens.
• Bonds are shared pairs of electrons, depicted as lines.
• 3D structure is a tetrahedron, optimizing bond distances.

Examples of Molecular Shapes

• Ammonia (NH₃): Pyramid shape.
• Carbon Dioxide (CO₂): Linear shape.
• Water (H₂O): Bent shape, like an elbow.
• Chlorine Trifluoride (ClF₃): T-shaped.

Experimental Verification

• Shapes predicted by models often match experimental results, though not always.

Complexity in Larger Molecules

• Large molecules like pharmaceuticals, DNA, proteins don't have an obvious central atom.
• Bonded atoms arrange to maximize attraction and minimize repulsion.

Molecules with Multiple Configurations

• Some molecules exhibit stable multiple configurations.
• Chemistry can arise from switching between these configurations without changing composition.