Chapter 4 Part B: Atoms and Elements

Learning Objectives

• Understand the periodic table in detail
• Learn about ions and atomic mass

The Periodic Table

Structure

• Divided into main elements and transition elements
• Groups and Periods:
  • Rows are called periods (elements have similar physical properties)
  • Columns are called groups (elements have similar chemical properties)
  • Groups have numbers, e.g., 1A, 2A, 3A, etc.
• Main elements include the first two and last six columns

Important Element Groups

• Halogens: Reactive nonmetals
• Noble Gases: Inert, stable electron configuration

Types of Elements

• Metals: Conduct electricity, solid at room temperature
• Nonmetals: Typically gases, poor conductors
• Metalloids: Have properties of both metals and nonmetals

Ions

• Formation of Ions: Adding/removing electrons affects charge, not mass
  • Cations: Positive ions (metals lose electrons)
  • Anions: Negative ions (nonmetals gain electrons)
• Charge Calculation:
  • Charge = Number of protons - Number of electrons
• Examples:
  • Chlorine gains an electron: 17 protons, 18 electrons, charge = -1
  • Sodium loses an electron: 11 protons, 10 electrons, charge = +1

Predicting Charges from the Periodic Table

• Metals (groups 1A, 2A, 3A) lose electrons and form positive ions
• Nonmetals gain electrons and form negative ions
• Transition elements have multiple possible charges

Atomic Mass

Definition and Calculation

• Atomic mass is a weighted average of the isotopic masses
• Mass Spectrometer used to determine isotopic masses
• Example Calculation:
  • Silicon has isotopes with masses 28, 29, 30 with given abundances
  • Weighted average = sum of (isotopic mass × relative abundance) / 100

Example Calculation

• Rubidium has isotopes 85 and 87
  • Calculate atomic mass using isotopic masses and abundances

Conclusion

• Reviewed detailed structure of the periodic table
• Understood formation and prediction of ion charges
• Calculated atomic mass from isotopic data

Proceed to Chapter 5