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AP CHEM UNIT 2

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Chapter 12: Properties and Bonding in Solids

12.1 General Characteristics of Solids

Solids are one of the fundamental states of matter, characterized by definite shape and volume. The properties of solids depend on the types of particles present and the forces holding them together.

  • Types of solids: Molecular, ionic, metallic, and covalent network solids.

  • Bonding: The nature of bonding (ionic, covalent, metallic, or intermolecular) determines the physical properties of solids.

  • Physical properties: Include melting point, hardness, electrical conductivity, and solubility.

12.3 Metallic Solids

Metallic solids consist of metal atoms held together by metallic bonding, which involves a 'sea' of delocalized electrons.

  • Bonding: Metal atoms share valence electrons freely, resulting in high electrical and thermal conductivity.

  • Properties: Malleability, ductility, luster, and high melting points.

  • Alloys: Mixtures of metals that can have improved properties compared to pure metals.

  • Example: Copper, iron, and steel are common metallic solids.

Additional info: For more on alloys, see: Bozeman Science: Metallic Solids

12.4 Metallic Bonding: Electron Sea Model

The electron sea model explains the unique properties of metals.

  • Malleability and ductility: Atoms can slide past each other without breaking bonds.

  • Conductivity: Free electrons allow metals to conduct electricity and heat efficiently.

12.5 Ionic Solids

Ionic solids are composed of cations and anions held together by strong electrostatic forces.

  • Bonding: Ionic bonds form between metals and nonmetals.

  • Properties: High melting and boiling points, brittle, conduct electricity when molten or dissolved in water.

  • Electrostatic attraction: The strength of attraction is described by lattice energy.

Lattice energy: The energy required to completely separate one mole of a solid ionic compound into its gaseous ions.

  • Coulomb's Law:

  • Larger charges and smaller ionic radii result in higher lattice energy.

12.6 Molecular Solids

Molecular solids are composed of molecules held together by relatively weak intermolecular forces.

  • Properties: Low melting and boiling points, often soft, poor conductors of electricity.

  • Examples: Ice, dry ice (solid CO2), sugar.

12.7 Covalent Network Solids

Covalent network solids consist of atoms connected by a continuous network of covalent bonds.

  • Properties: Very high melting points, hard, often poor conductors.

  • Examples: Diamond (carbon), quartz (SiO2).

Covalent Bonding in Solids

  • Bonding network: Explains strength, hardness, and high melting/boiling points.

Chapter 8: Chemical Bonding

8.1 Lewis Structures and the Octet Rule

Lewis structures are diagrams that show the bonding between atoms and the lone pairs of electrons in a molecule.

  • Octet rule: Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.

  • How to draw: Count valence electrons, arrange atoms, distribute electrons to satisfy the octet rule.

8.2 Ionic Bonding

Ionic bonding occurs between metals and nonmetals, involving the transfer of electrons from cations to anions.

  • Prediction of charges: Based on group number in the periodic table.

  • Bond energy: Related to lattice energy; higher lattice energy means stronger ionic bonds.

8.3 Covalent Bonding

Covalent bonds form when two atoms share one or more pairs of electrons.

  • Orbital overlap: Covalent bonds result from the overlap of atomic orbitals.

  • Electron pairs: Shared between atoms to achieve stable electron configurations.

8.4 Polarity of Covalent Bonds

Covalent bonds can be polar or nonpolar depending on the difference in electronegativity between the bonded atoms.

  • Nonpolar bonds: Electrons are shared equally.

  • Polar bonds: Electrons are shared unequally, resulting in partial charges.

  • Electronegativity: The ability of an atom to attract electrons in a bond.

  • Dipole moment: A measure of bond polarity.

8.5 Lewis Structures for Covalent Compounds

Lewis structures help visualize the arrangement of atoms and electrons in molecules.

  • Rules: Follow the octet rule, use single, double, or triple bonds as needed.

  • Polyatomic ions: Account for overall charge when drawing structures.

  • Formal charge: Used to determine the most likely structure.

  • Resonance: Some molecules have multiple valid Lewis structures; the actual structure is a hybrid.

8.7 Exceptions to the Octet Rule

Some atoms do not follow the octet rule.

  • Odd number of electrons: Some molecules have an odd number of electrons (free radicals).

  • Expanded octet: Elements in period 3 or higher can have more than 8 electrons around the central atom.

  • Examples: PCl5, SF6, XeF4.

8.8 Bond Energy and Bond Length

Bond energy is the energy required to break a bond. Bond length and strength vary with atomic radius and bond order.

  • Bond order: Single (one sigma bond), double (one sigma and one pi bond), triple (one sigma and two pi bonds).

  • Bond length: Decreases as bond order increases.

  • Bond strength: Increases as bond order increases.

Electron Domain Geometry and Molecular Polarity

The shape of a molecule is determined by the number of electron domains (regions of electron density) around the central atom.

# Electron Domain

# Lone Pairs (LP)

Name

2

0

Linear

3

0

Trigonal planar

3

1

Bent

4

0

Tetrahedral

4

1

Trigonal pyramidal

4

2

Bent

5

0

Trigonal bipyramidal

5

1

Seesaw

5

2

T-shaped

5

3

Linear

6

0

Octahedral

6

1

Square pyramidal

6

2

Square planar

Determining Molecular Polarity

  • Check for polar bonds (difference in electronegativity).

  • If polar bonds are present, consider the molecular geometry:

    • If dipoles cancel (symmetrical geometry), the molecule is nonpolar.

    • If dipoles reinforce (asymmetrical geometry), the molecule is polar.

Hybridization and Bonding

Hybridization explains the observed shapes of molecules by mixing atomic orbitals to form new hybrid orbitals.

  • sp: Linear geometry (2 electron domains)

  • sp2: Trigonal planar geometry (3 electron domains)

  • sp3: Tetrahedral geometry (4 electron domains)

Bond Order and Types of Bonds

  • Single bond: One sigma (σ) bond

  • Double bond: One sigma and one pi (π) bond

  • Triple bond: One sigma and two pi bonds

Additional Resources

  • YouTube: Covalent Bonding

  • YouTube: Hybridization

Additional info: Some content was inferred and expanded for clarity and completeness, including definitions, examples, and explanations of key terms and concepts.

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