Lecture Summary: Understanding Subatomic Particles, Isotopes, and Ions

Subatomic Particles in Atoms

• Three main subatomic particles: Protons, Neutrons, and Electrons.
• Protons: Positively charged; define an element's identity (e.g., Carbon has 6 protons).
• Neutrons: Neutral; their variation changes the mass, resulting in different isotopes.
• Electrons: Negatively charged; variations result in ions with electrical charges.

Understanding Ions

• Atoms become ions when their number of electrons changes, not their protons.
• Cations: Positively charged ions, have fewer electrons than protons.
  • Example: Sodium ion (Na⁺) has lost an electron, resulting in one more proton than electrons.
• Anions: Negatively charged ions, have more electrons than protons.
  • Example: Chlorine ion (Cl⁻) has gained an electron, resulting in one more electron than protons.

Charges and Terminology

• Positive ions (Cations): Indicated by fewer electrons than protons.
• Negative ions (Anions): Indicated by more electrons than protons.
• Battery analogy: Positive terminal (cathode) corresponds with cations; negative terminal (anode) corresponds with anions.

Examples and Practice

Determining Ion Composition

1. Sodium (Na⁺):
   • 11 protons, 10 electrons (positive charge due to one less electron).
2. Chlorine (Cl⁻):
   • 17 protons, 18 electrons (negative charge due to one extra electron).
3. Oxygen (O²⁻):
   • 8 protons, 10 electrons (2 extra electrons).
4. Aluminum (Al³⁺):
   • 13 protons, 10 electrons (3 more protons than electrons).
5. Phosphorus (P³⁻):
   • 15 protons, 18 electrons (3 extra electrons).

Writing Ionic Symbols

• Correct format for ionic charge: Number followed by the charge sign (e.g., 2⁺, not +2).
• Example: Calcium ion with 20 protons and 18 electrons is written as Ca²⁺.

Isotopic Symbol and Charge Calculation

• Example 1: Chlorine-37 with 1 negative charge:
  • 17 protons, 20 neutrons, 18 electrons.
• Example 2: Magnesium with 12 protons:
  • 12 protons, 13 neutrons, 10 electrons (Mg²⁺).
• Example 3: Lead with 82 protons, 4 positive charge:
  • 82 protons, 126 neutrons, 78 electrons.
• Example 4: Phosphorus with 15 protons and 33 mass number:
  • 15 protons, 18 neutrons, 18 electrons (P³⁻).

Key Takeaways

• Changing the number of protons changes the element identity.
• Ionic charge is determined by the balance of protons and electrons.
• Always write the ionic charge with the number first (e.g., 3⁺).
• Practice identifying ion compositions and writing correct ionic symbols.