Atoms, Molecules, and Ions

2.1 Atomic Theory of Matter

• Early Beliefs:

  • Greek philosopher Democritus proposed that everything is made of indivisible particles called "atomos" (meaning uncuttable).

• Organized Atomic Theory by Dalton:

  • Established in the late 1700s and early 1800s.
  • Supported by several key laws:
  • Law of Constant Composition: Compounds always contain the same proportion of elements.
  • Law of Conservation of Mass: Mass is conserved in chemical reactions.
  • Law of Multiple Proportions: If two elements form multiple compounds, their masses combine in small whole-number ratios.

2.2 Discovery of Subatomic Particles

• Dalton's Perspective: Atoms were once considered the smallest particles.
• Advances in science revealed that atoms consist of subatomic particles. Key discoveries included:
  1. Electrons from Cathode Rays: J.J. Thomson discovered cathode rays are streams of negatively charged particles.
  2. Radioactivity: Henri Becquerel's observed spontaneous emission of radiation which led to a better understanding of atomic structure.
  3. Nucleus: Through experiments by Ernest Rutherford, atoms were revealed to have a dense central nucleus (with protons and neutrons).

2.3 Atomic Structure - The Modern View

• Structure: The atom includes a nucleus surrounded by electrons.
• Protons (+1 charge) and neutrons (neutral) reside in the nucleus, while electrons (-1 charge) orbit around it.
• Mass Comparison: Protons and neutrons have a similar mass (about 1 amu), whereas the electron mass is negligible (~5.486 imes 10^{-4} amu).

2.4 Atomic Mass Unit (amu)

• The atomic mass scale is based on the mass of carbon-12 (12C = 12 amu).
• 1 amu = 1.66054 imes 10^{-24} grams.

2.5 Periodic Table

• Elements are organized by atomic number and grouped based on similar properties.
• Periods: Rows in the table (1-7).
• Groups: Columns in the table with similar chemical properties. Examples include:
  • Group 1A: Alkali Metals (Li, Na, K, etc.)
  • Group 2A: Alkaline Earth Metals (Be, Mg, Ca, etc.)
  • Group 6A: Chalcogens (O, S, Se, etc.)
  • Group 7A: Halogens (F, Cl, Br, etc.)
  • Group 8A: Noble Gases (He, Ne, Ar, etc.)

2.6 Molecules and Molecular Compounds

• Chemical Formula: Indicates the number of atoms in a molecule (e.g., H_2O for water).
• Types of Compounds:
  1. Molecular Compounds: Composed mostly of nonmetals.
  2. Ionic Compounds: Formed from metals and nonmetals.

2.7 Ions and Ionic Compounds

• Ions: Charged particles formed when atoms lose or gain electrons.
  • Cations: Positively charged (form from loss of electrons, typically metals).
  • Anions: Negatively charged (form from gain of electrons, typically nonmetals).
• Ionic Compounds: Compounds formed from the attraction between cations and anions (e.g., NaCl).

2.8 Naming Inorganic Compounds

• Nomenclature: Systematic naming of chemical compounds based on the type of ions.
  • Cations take the element name, while anions take an "-ide" ending for single-atom anions.
• Common Ions (Table 2.4 & 2.5): List of essential cations and anions for memorization.

2.9 Some Simple Organic Compounds

• Organic Chemistry: The study of carbon compounds, focusing on hydrocarbons and their derivatives (e.g., alcohols).
• Naming: Derived from the alkane name with functional group modifications (e.g., alcohols end in "-ol").