lecture #2

Chapter 2: Atoms, Molecules, and Ions

Dalton’s Atomic Theory

  • Postulates: Structure of matter explained by combinations of small particles.

    • All matter is composed of indivisible atoms.

    • Atoms retain their identity during chemical reactions.

    • Element: Type of matter made of only one kind of atom.

  • Compounds: Matter made of two or more elements combined in fixed proportions.

  • Chemical Reactions: Rearrangement of atoms in reactants to form new substances.

Atomic Symbols

  • Notation: A one or two-letter representation of an atom corresponding to an element.

    • Derived from the element's name, often in another language.

    • Convention: First letter capitalized, second letter lowercase.

Law of Multiple Proportions

  • When two elements form more than one compound, the masses of one element in these compounds, for a fixed mass of the other element, are in small whole number ratios.

  • Example:

    • Compound 1: CO (1 gram C + 1.3321 grams O2)

    • Compound 2: CO2 (1 gram C + 2.6642 grams O2)

Atomic Structure

  • Parts of the Atom:

    • Nucleus: Central core, positively charged, contains most of the atom's mass.

    • Electrons: Negatively charged, very light, found in the region around the nucleus.

Discovery of the Electron

  • J.J. Thomson:

    • Used cathode-ray tubes to prove that atoms aren’t indivisible.

    • Most matter contains electrons, calculating the mass-to-charge ratio of electrons.

Nuclear Model of the Atom

  • Ernest Rutherford's Experiment:

    • Bombarded thin gold foil with alpha particles.

    • Most alpha particles passed through; some scattered at large angles.

    • Proposed that the nucleus contains 99.95% of an atom's mass.

Fundamental Particles

  • Protons:

    • Positively charged, mass more than 1800 times that of electrons.

    • Atomic number (Z): Number of protons in an atom.

  • Neutrons:

    • Electrically neutral, similar mass to protons.

    • Mass number (A): Total number of protons plus neutrons.

Nuclides and Isotopes

  • Nuclide: Characterized by atomic number (Z) and mass number (A).

  • Isotopes: Atoms with the same atomic number but different mass numbers (different neutrons).

Atomic Weights

  • Relative Atomic Weights: Average mass of an atom relative to another.

    • Atomic Mass Unit (amu): Mass equal to one-twelfth of a carbon-12 atom.

  • Atomic Weight: Average atomic mass of a naturally occurring element.

Mass Spectrometry

  • Calculating atomic weight and isotopic masses, as well as fractional abundance of isotopes.

Periodic Table Basics

  • Arrangement of elements in rows (periods) and columns (groups) showcasing periodicity of properties.

  • IUPAC Numbering: Columns numbered from 1 to 18.

  • Types of Elements:

    • Metals: Luster, good conductors of heat and electricity.

    • Nonmetals: Lack metallic properties.

    • Metalloids: Exhibit characteristics of both.

Chemical Formulas

  • Notation: Uses symbols with subscripts to denote relative amounts of atoms in a substance.

Molecules and Polymers

  • Molecule: Group of chemically bonded atoms.

  • Molecular Formula: Indicates number of each type of atom.

  • Polymer: Large molecule made of repeating smaller molecules (monomers).

Ions

  • Definition: Charged particle from an atom or group of atoms by electron loss/gain.

  • Cation: Positively charged ion (e.g., sodium ion Na+).

  • Anion: Negatively charged ion (e.g., chloride ion Cl–).

Ionic Compounds

  • Made of cations and anions; conducted through ionic bonds.

  • Formula represents smallest amount of ions for neutrality.

  • Example: Chromium (III) Oxide - Cr2O3, combination of Cr3+ ions and O2– ions.

Organic Compounds

  • Molecular substances containing carbon, hydrogen, and possibly other elements (O, N).

  • Hydrocarbons: Compounds consisting solely of C and H.

  • Functional groups: Specific reactive portions of molecules.

Chemical Nomenclature

  • Systematic naming of chemical compounds.

  • Qualifiers: Prefixes or suffixes often denote charge or groups in nomenclature.

  • Inorganic Compounds: Include elements other than carbon (e.g., carbonates).

Naming Ions and Compounds

  • Cation naming first, followed by anion.

  • Monatomic ions derive from a single atom; -ide suffix for anions (e.g., Br- → bromide ion).

  • Multi-Cation Ions: Named with roman numeral or suffix –ic/-ous.

  • Polyatomic Ions: Consist of multiple atoms combined and charged.

Chemical Equations

  • Symbolic representation of chemical reactions.

  • Reactants on left, Products on right.

  • Balancing: Ensure equal numbers of each atom on both sides.

  • Method: Count atoms and apply coefficients for balance.

Hydrates

  • Compounds containing water molecules in their formula (e.g., CuSO4·5H2O).

  • Nomenclature includes the number of water molecules.

  • Example: Epsom salts - MgSO4·7H2O.