Overview
This lecture covers the concept of ions, distinguishing between cations and anions, and explains how atoms form ions by gaining or losing electrons.
Definition and Classification of Ions
- An ion is any charged particle, including both charged atoms and charged molecules.
- Ions are classified into two types: cations (positively charged) and anions (negatively charged).
- Cations are positively charged because they have lost electrons.
- Anions are negatively charged because they have gained electrons.
Formation of Cations
- Atoms form cations by losing electrons.
- The number of electrons lost equals the positive charge of the cation.
- Example: Sodium (Na), atomic number 11, forms Na⁺ (11 protons, 10 electrons).
- Example: Calcium (Ca), atomic number 20, forms Ca²⁺ (20 protons, 18 electrons).
- Example: Aluminum (Al), atomic number 13, forms Al³⁺ (13 protons, 10 electrons).
Formation of Anions
- Atoms form anions by gaining electrons.
- The number of electrons gained equals the negative charge.
- Example: Chlorine (Cl), atomic number 17, forms Cl⁻ (17 protons, 18 electrons).
- Example: Nitrogen (N), atomic number 7, forms N³⁻ (7 protons, 10 electrons).
- Example: Oxygen (O), atomic number 8, forms O²⁻ (8 protons, 10 electrons).
Charge Notation in Chemistry
- In chemistry, the magnitude of the charge is written first, followed by the sign (e.g., 2⁺, 3⁻).
- Charges are written as superscripts on the right side of the element symbol.
Key Terms & Definitions
- Ion — a charged atom or molecule.
- Cation — an ion with a positive charge, formed by losing electrons.
- Anion — an ion with a negative charge, formed by gaining electrons.
- Proton — positively charged particle in the nucleus; defines the element's identity.
- Electron — negatively charged particle orbiting the nucleus.
Action Items / Next Steps
- Practice determining the number of protons and electrons for given ions using the periodic table.
- Review charge notation by writing ions with correct superscript format.