Molecular Compounds - Chapter 8

Overview

• Atoms can form molecular compounds by sharing electrons, creating covalent bonds.
• Molecular compounds differ from ionic compounds in melting and boiling points.
• Molecular formulas provide information on the number and types of atoms in a molecule.

Key Concepts

• Covalent Bond: A chemical bond formed by the sharing of electrons between atoms.
• Molecule: A group of atoms bonded together by covalent bonds.
• Diatomic Molecule: A molecule consisting of two atoms.
• Molecular Compound: A compound composed of molecules.
• Molecular Formula: Shows the number and type of atoms in a molecule.

Molecular Compounds vs. Ionic Compounds

• Molecular compounds generally have lower melting and boiling points compared to ionic compounds.
• Ionic compounds form crystalline solids with high melting points.
• Mixtures of nonmetals typically form molecular compounds.

Examples

• Water (H₂O): Two hydrogen atoms and one oxygen atom.
• Carbon Monoxide (CO): One carbon atom and one oxygen atom.

Nature of Covalent Bonding

• Octet Rule: Atoms share electrons to achieve noble gas electron configurations.
• Single Covalent Bond: Formed when two atoms share one pair of electrons.
• Double and Triple Bonds: Atoms share two or three pairs of electrons respectively.

Special Bonds

• Coordinate Covalent Bond: One atom contributes both electrons in a shared pair.
• Resonance Structures: Molecules like ozone can be represented by multiple electron dot structures.

Bonding Theories

• VSEPR Theory: Predicts molecular shapes based on electron pair repulsion.
• Molecular Orbitals: Atomic orbitals combine to form molecular orbitals, facilitating bonding.
• Hybridization: Mixing of atomic orbitals to form new hybrid orbitals for bonding.

Polar Bonds and Molecules

• Polar Covalent Bond: Uneven sharing of electrons between atoms with different electronegativities.
• Dipole: A molecule with two poles due to uneven distribution of electrons.
• Intermolecular Forces: Include van der Waals forces, dipole interactions, dispersion forces, and hydrogen bonds.
• Network Solids: Solids with atoms connected by covalent bonds throughout the material; have high melting points (e.g., diamond).

Conclusion

• Molecular compounds display a wide range of physical properties due to differing intermolecular forces.
• Understanding covalent bonding and molecular structure is essential for predicting the behavior of substances in different conditions.