Review of Lecture Notes on Atomic Theory and Calculations

Overview of Course Content

  • Emphasis on Historical Knowledge

    • The course will include significant historical figures in science.

    • Important names will be highlighted in blue for memorization.

    • Names in black are non-essential.

  • Importance of Calculating Large and Small Numbers

    • Be familiar with using scientific calculators for calculations involving exceedingly large or small numbers.

    • Example provided of a constant defined to nine significant figures.

    • Understanding the energy of photons in relation to the frequency of electromagnetic waves.

Calculator Usage

  • Students are required to master the use of a scientific calculator.

    • Types of Calculator: No graphing or phone calculators permitted during exams.

    • Affordability: Scientific calculators can be purchased for $10-$20.

    • Impact on Exams: Lack of familiarity with calculators may negatively affect performance on tests.

Example Calculation

  • Energy Calculation involving Electromagnetic Waves

    • Given Frequency: 500 megahertz.

    • Convert to hertz: 500 MHz = 500 imes 10^6 Hz.

    • Photon Energy Equation: Use the formula relating energy (E) to frequency.

    • Result calculation ends with the energy of the photon being E = 3.31 imes 10^{-25} ext{ joules per photon}.

  • Pedagogical Techniques:

    • Step-By-Step Calculator Instructions:

    • Key sequence demonstrated for inputting calculations correctly, emphasizing proper use of parentheses.

    • Variations in button pressing sequences on different calculators.

Historical Figures in Atomic Theory

  • Dmitry Mendeleev

    • Background: Russian scientist from the late 1800s; youngest of 14 children.

    • Academic Journey: Moved to Moscow for university; struggled initially but succeeded in academia and published groundbreaking work in organic chemistry.

    • Periodic Table Dream: Dreamed about a systematic arrangement of elements, leading to the creation of the periodic table.

    • Predictions: Anticipated gaps in the periodic table and correctly predicted properties of undiscovered elements.

  • Contribution and Recognition: Nominated nine times for the Nobel Prize; not awarded due to political reasons.

Key Historical Development of Atomic Theory

  • Historical Understanding of Matter: The concept of the atom has evolved over centuries, from ancient philosophers through modern chemistry.

Early Postulates of Atomic Theory by John Dalton (Early 1800s)

  • Matter is composed of atoms.

  • Atoms are indivisible, though later proven inaccurate.

  • Atoms of the same element are identical; no two different elements have identical mass.

  • Compounds form in whole number ratios of elements.

Notable Laws and Experiments

  • Law of Definite Proportions (Joseph Kraus, 1793)

    • Fixed mass ratios exist in compounds, illustrated with sodium chloride (NaCl).

  • Dalton's Multiple Proportions

    • Elements may form multiple compounds with fixed atomic ratios.

Chemical Reactions and Stoichiometry

  • Chemical reactions rearrange atoms, but significant discrepancies arose during Dalton's time, requiring the law of combining volumes (Gay-Lussac).

  • Avogadro's Hypothesis: Explains diatomic molecules contributing to understanding gas behavior in reactions.

Significant Experiments in Atomic Theory

  • JJ Thomson's Cathode Ray Tube Experiment (1897)

    • Demonstrated electrons as negatively charged particles.

    • Established model of the atom with electrons embedded in a positively charged mass.

  • Millikan's Oil Drop Experiment

    • Determined the charge of the electron as 1.6 imes 10^{-19} Coulombs and related to its mass.

  • Ernest Rutherford's Gold Foil Experiment (1910)

    • Discovered the atomic nucleus by bombarding gold foil with alpha particles, which revealed a concentrated positive charge.

    • Postulated the existence of neutrons to maintain atomic stability by balancing protons’ positive charges and preventing electromagnetic repulsion.

Current Understanding of Atomic Structure

  • Structure of the Atom Today:

    • Nucleus composed of protons and neutrons, held together by the strong nuclear force.

    • Electrons exist in a cloud around the nucleus, significantly large in volume compared to the nucleus.

    • Atomic and Nuclear Radii:

    • Atomic radius: approximately 1 nanometer.

    • Nuclear radius: approximately 5x10^{-15} meters.

  • Atomic Notation:

    • Components: Symbol (X), Atomic Number (Z), and Mass Number (A).

    • Example for Beryllium:

      • Symbol: Be; Atomic Number: 4 (4 protons); Mass Number: 8 (p+n).

  • Isotopes:

    • Variants of elements with differing neutron counts but the same proton count, affect mass number while maintaining similar chemical properties.

Practical Examples

  • Example Questions

    • Calculation for iron raising the atomic number (Fe) and comparison against isotopes like carbon (C) and oxygen (O).

Conclusion

  • Ongoing understanding of atomic theory shaped by historical figures and experiments.

  • Importance of mastering calculations, atomic theory background, and nomenclature for success in chemistry.