Ch 13: Inside the Atom

Sub-atomic Particles

• Protons:

  • Located in the nucleus of the atom
  • Charge: +1 (positive)

• Neutrons:

  • Also found in the nucleus
  • Charge: Neutral (no electric charge)

• Electrons:

  • Orbit around the nucleus in specific energy levels or shells
  • Charge: -1 (negative)

Atomic Number and Mass Number

• Atomic Number (Z):

  • Represents the number of protons in the nucleus
  • Identifies a chemical element uniquely (e.g., Carbon has Z = 6)

• Mass Number (A):

  • Total number of protons and neutrons in the nucleus
  • Calculated using the formula: A = Z + N (where N is the number of neutrons)

Calculating Protons, Neutrons, and Electrons

• Number of Protons (p): Equal to the atomic number (Z)
• Number of Neutrons (n): Calculated by n = A - Z
• Number of Electrons (e): Equal to the number of protons in a neutral atom

Valence Electrons and Electron Configuration

• Argon (Ar):

  • Atomic number: 18
  • Electron configuration: 2, 8, 8
  • Valence electrons: 8

• Aluminum (Al):

  • Atomic number: 13
  • Electron configuration: 2, 8, 3
  • Valence electrons: 3

• Oxygen (O):

  • Atomic number: 8
  • Electron configuration: 2, 6
  • Valence electrons: 6

Atomic Structure from Bohr’s Model

• Element with Z = 20:

  • Mass number (A): 40
  • Protons: 20
  • Neutrons: 20
  • Electrons: 20

• Element with Z = 11:

  • Mass number (A): 23
  • Protons: 11
  • Neutrons: 12
  • Electrons: 11

Distinctions Between Atoms, Ions, Molecules, Compounds, and Mixtures

• Atoms:

  • Smallest unit of an element retaining its chemical properties
  • Example: Hydrogen (H), Carbon (C)

• Molecules:

  • Two or more atoms bonded together
  • Same element example: Oxygen (O₂)
  • Different elements example: Water (H₂O)

• Ions:

  • Atoms or molecules with a net electrical charge due to loss or gain of electrons
  • Cations: Positively charged (e.g., Na⁺)
  • Anions: Negatively charged (e.g., Cl⁻)

• Compounds:

  • Formed by chemically bonded different elements
  • Unique properties compared to individual elements
  • Example: Sodium chloride (NaCl), Carbon dioxide (CO₂)

• Mixtures:

  • Combination of two or more substances that are not chemically bonded
  • Components retain individual properties
  • Example: Saltwater (homogeneous), Sand and iron filings (heterogeneous)

Writing Chemical Formulae

• Atoms:

  • H₂O: Two hydrogen atoms + One oxygen atom
  • CO₂: One carbon atom + Two oxygen atoms

• Simple Ionic Compounds:

  • Ca²⁺ + Cl⁻ → CaCl₂
  • Mg²⁺ + Br⁻ → MgBr₂
  • Al³⁺ + S²⁻ → Al₂S₃

• Polyatomic Ions:

  • Interaction involves complex ions with multiple atoms that carry a charge.