Developing a Nuclear Model of the Atom

Developing a Nuclear Model of the Atom

Section 3.1

History of Atomic Theory

• Overview of key contributors to atomic theory:

  • Dalton (1803)

  • Thomson (1904) - positive and negative charges

  • Rutherford (1911) - nucleus

  • Bohr (1913) - energy shells

  • Schrödinger (1926) - electron cloud model

Key Models of the Atom

Electron Cloud Model

• Darker areas indicate higher probability of finding electrons.

  • Nucleus represents the center with positive charge.

JJ Thomson's Model

• Spherical cloud of positive charge with embedded electrons.

Rutherford's Experiment

• Setup includes:

  • Detecting screen

  • Gold foil

  • Alpha particle emitter.

Rutherford's Model Limitations

• Missing explanation for electron behavior and stability.

Energy Levels in Atoms

Bohr's Atomic Model

• Electrons orbit the nucleus in fixed energy levels (n = 1, 2, 3, 4).

• Electrons can move between levels by absorbing or releasing energy.

Spectra and Energy Levels

• Continuous Spectrum vs. Emission Line Spectrum

• Energy release occurs when electrons fall back to ground state.

Understanding Isotopes

Isotope Notation

• Mass number (A) = Number of protons + Number of neutrons

• Example: Carbon-12: 6 protons, 6 neutrons.

Average Atomic Mass Calculation

• Calculation involves:

  • Contribution of each isotope's mass based on abundance.

• Example for Zinc:

  • Zn-64 contributes 31.07 u

  • Zn-66 contributes 18.39 u

  • Summation of contributions for average atomic mass.

Conclusion

• A comprehensive understanding of atomic structure includes historical models, limitations, and the role of isotopes in calculating average atomic mass.