**Chemistry Class Notes**
**Date: August 4, 2024**
**Topic: Atomic Structure and the Periodic Table**
1. **Atoms: Basic Unit of Matter**
- Comprised of protons (+), neutrons (neutral), electrons (−)
- Nucleus: protons + neutrons
- Electron cloud: region where electrons orbit the nucleus
2. **Subatomic Particles**
- **Protons:**
- Charge: +1
- Mass: 1 amu (atomic mass unit)
- Determines atomic number (Z)
- **Neutrons:**
- Charge: 0
- Mass: 1 amu
- Isotopes: atoms of the same element with different neutron counts
- **Electrons:**
- Charge: −1
- Mass: ~0 amu
- Balance the charge of protons
3. **Atomic Number (Z)**
- Number of protons in an atom
- Defines the element (e.g., Z=6 is carbon)
4. **Mass Number (A)**
- Total number of protons + neutrons
- A = Z + N (N = neutrons)
- Example: Carbon-12 (6 protons, 6 neutrons), Carbon-14 (6 protons, 8 neutrons)
5. **Electron Configuration**
- Distribution of electrons in atomic orbitals
- **Energy Levels:** 1, 2, 3, etc.
- **Sublevels:** s, p, d, f
- s: 2 electrons
- p: 6 electrons
- d: 10 electrons
- f: 14 electrons
- Aufbau Principle: Electrons fill from lowest to highest energy levels
6. **Periodic Table Overview**
- Organized by increasing atomic number
- Rows = Periods (properties change progressively)
- Columns = Groups/Families (similar properties)
- **Main Groups:**
- Group 1: Alkali Metals (e.g., Na, K)
- Group 2: Alkaline Earth Metals (e.g., Mg, Ca)
- Groups 13-18: Transition and main group elements
7. **Trends in the Periodic Table**
- **Atomic Radius:** Decreases across a period, increases down a group
- **Ionization Energy:** Increases across a period, decreases down a group
- **Electronegativity:** Tendency of an atom to attract electrons; increases
across a period, decreases down a group
8. **Ions**
- Atoms can gain or lose electrons to form ions
- **Cations:** positively charged (loss of e⁻)
- **Anions:** negatively charged (gain of e⁻)
- Example: Na → Na⁺ (loses 1 e⁻), Cl → Cl⁻ (gains 1 e⁻)
9. **Practice Problems:**
- Determine the number of protons, neutrons, and electrons in various isotopes.
- Write electron configurations for elements in Groups 1, 2, and 17.
- Identify trends in atomic size and ionization energy across periods.
**Homework:**
- Read Chapter 2 (Atomic Structure)
- Complete problems 1-10 at the end of the chapter
**End of Notes**
