Chemistry Lecture Notes

Introduction

• Atoms: Everything is made of atoms, even you.
  • Atoms consist of a core (protons and neutrons) and electrons.
  • Different elements are characterized by different numbers of protons.

Structure of Atoms

• Core: Made of protons and neutrons.
• Electrons: Orbit the core in multiple electron shells.
  • Outermost shell electrons are called valence electrons.
  • Most of chemistry deals with the behavior of these electrons.
• **Elements in the periodic table: **
  • Grouped by the number of valence electrons.
  • Period number signifies the number of electron shells.

Periodic Table Insights

• Periodic table: Lists all elements
  • Columns (groups) have elements with the same number of valence electrons.
  • Rows (periods) have elements with the same number of electron shells.
  • Atomic mass increases from left to right.
  • Groups such as Alkali Metals all have similar properties (e.g., one valence electron).
  • **Special Cases: **
    • Helium only has 2 electrons but is grouped with noble gases.

Isotopes and Ions

• Isotopes: Atoms of the same element with different numbers of neutrons; unstable ones emit ionizing radiation.
• Ions: Charged atoms
  • Equal electrons and protons: no charge
  • More electrons: negative charge (anions)
  • Less electrons: positive charge (cations)

Molecular Composition

• Molecules: Two or more atoms bonded together
• Compounds: Molecules consisting of at least two different elements.
• **Bonding Types: **
  • Ionic Bonds: Transfer of electrons (e.g., Sodium Chloride).
  • Covalent Bonds: Sharing of electrons.
    • Nonpolar Covalent Bonds: Equal sharing (e.g., Cl2).
    • Polar Covalent Bonds: Unequal sharing (e.g., H2O).
  • Metallic Bonds: Delocalized electrons in metal grids.

Intermolecular Forces (IMFs)

• Dipoles: Permanent electric dipoles occur in polar molecules (e.g., H2O).
  • IMFs attract molecules to each other.
  • Hydrogen Bonds: Occur when hydrogen is bonded to F, O, or N.
  • Van der Waals Forces: Temporary dipoles due to electron motion.
• Solubility:
  • Polar solvents dissolve polar substances.
  • Nonpolar solvents dissolve nonpolar substances.

States of Matter

• Solids: Tightly packed particles with fixed structure.
• Liquids: Free-moving particles in a fixed volume.
• Gases: Particles with enough energy to fill any volume.
• Plasma: Ionized gas at very high temperatures or electric potential.

Temperature and Entropy

• Temperature: Average kinetic energy of particles.
• Entropy: Amount of disorder:
  • Low entropy in solids (neatly organized).
  • High entropy in gases.
• Phase Changes: Depend on temperature and pressure (e.g., ice melting at >0°C).

Chemical Reactions

• **Types: **
  • Synthesis
  • Decomposition
  • Single Replacement
  • Double Replacement
• Activation Energy: Energy needed to start a reaction.
• Catalysts: Lower the activation energy.
• **Enthalpy: **
  • Exothermic: Reaction releases heat.
  • Endothermic: Reaction absorbs heat.
• Equilibrium: Reversible reactions at same speed in both directions.

Acids and Bases

• Acid-Base Behavior: According to Brønsted-Lowry:
  • Acids donate protons (H+).
  • Bases accept protons.
  • Amphoteric: Molecules act as both acid and base.
• Strength Measurement:
  • pH: Concentration of H3O+ ions (lower pH = more acidic).
  • pOH: Concentration of OH- ions.

Quantum Mechanics and Electrons

• **Quantum Numbers: **
  • n: Shell number
  • l: Shape of orbital
  • ml: Orientation of orbital
  • ms: Spin of electron
• **Orbitals and Subshells: **
  • s, p, d, f subshells holding different numbers of electrons.
  • Electron configuration follows Aufbau principle.
• Pauli Exclusion Principle: No two electrons can have the same four quantum numbers.

Closing

• Summary of key points about atomic structure and behavior.
• Importance of understanding electrons and their configurations.