Chemistry Lecture Review

The class is nearing its conclusion with significant discussion around final preparations and topics.
- Focus on the final exam and completion of homework.
- Encourage reliance on worksheets as primary study material.

Reminders about the nature of the upcoming final exam:
- It will cover thermal chemistry and solids, primarily from Chapters 9 and 10.
- The final is not comprehensive, focusing on contents covered since Exam 2.
Date and time of final exam: Saturday, May 3, at 1:30 PM to 4:00 PM.
Students not taking the exam in class must notify the instructor regarding seating arrangements in the testing center.

Polymorphic Materials: Same material can have different structures leading to distinct properties.
- Example: Carbon can exist as diamond or graphite.
- Diamond is hard, transparent, and reflects light due to its structure.
- Graphite is opaque and slippery due to layered arrangement of benzene rings

Diamond:
- Hardest naturally occurring material
- High refractive index, making it sparkle
- Insulator with high thermal conductivity due to tightly packed structure.
Graphite:
- Conducts electricity due to delocalized electrons in s and p orbitals.
- Used as a lubricant due to layered structure making it slippery.
Stability:
- Graphite is more stable under normal conditions compared to diamond, which requires high pressure and heat to form.

Interest in materials for electronics and alternatives to metals (like copper) due to conductivity differences.
Discussion on semiconductors:
- Metals have conductivity that decreases with increased temperature; this is not the case for semiconductors.
Silicon: Abundant in earth's crust and utilized for computer chips; must be ultra-pure for functionality.

Introduction of impurities (e.g., boron for p-type and phosphorus for n-type doping) creates charge carriers (holes/electrons).
Important for the function of semiconductor devices.

Solutions are homogeneous mixtures consisting of solute(s) dissolved in a solvent.
Key concentration measures:
- Molarity: Moles of solute per liter of solution.
- Molality: Moles of solute per kilogram of solvent.
- Mass Percent: Mass of solute divided by mass of solution multiplied by 100.
- Mole Fraction: Moles of component divided by total moles in the mixture.

Henry's Law: Describes gas solubility in liquids under pressure; solubility increases with pressure.
Example of practical use: Carbonated beverages and implications for scuba diving.

Enthalpy changes associated with dissolution processes:
- Requires energy input to separate solute and solvent.
- Described by Hess's law, combining energy changes of the process.

Memorize the differences between diamond and graphite.
Understand the significance of doping in semiconductors.
Familiarize with various units of concentration as they are used in calculations regarding solutions.
Review key laws like Henry's Law and their applications to real-world scenarios of gases dissolved in liquids.