Comprehensive Study Guide: Atomic Structure, History, and Calculations

Early Atomic Philosophy and the First Atomic Theory

• Democritus (400 B.C.): First proposed the concept of atoms; no experimental evidence.

• John Dalton (1766-1844): Provided postulates for atomic theory:   1. 5Indivisible particles called atoms.   2. Atoms of the same element are identical; different from those of other elements.   3. Atoms combine in whole number ratios.   4. Atoms cannot change into other atoms in chemical reactions.

Discovery of Subatomic Structure

• J.J. Thomson: Discovered the electron via the cathode ray tube experiment; proposed the Plum Pudding Model.

• Ernest Rutherford: Discovered the nucleus through the Gold Foil Experiment, concluded:   1. Atoms are mostly empty space.   2. Nucleus is dense and small with a positive charge.

Subatomic Particles and Their Properties

• Electron: Charge: -1; Relative Mass: 1/1840.

• Proton: Charge: +1; Relative Mass: 1.

• Neutron: Charge: 0; Relative Mass: 1.

Defining the Atom: Numbers and Identities

• Atomic Number: Number of protons; identifies the element.

• Mass Number: Total number of protons and neutrons.

• Neutral Atoms: Equal number of protons and electrons.

Isotopes and Ions

• Isotopes: Same protons, different neutrons.

• Ions: Charged atoms formed by losing or gaining electrons;   - Cations: Positive charge (lose electrons).   - Anions: Negative charge (gain electrons).

Element Abbreviations and Atomic Math Summary

• Mass Number and Atomic Number notation; include charge representation.

• Key formulas:   - Atomic Number = Protons = Electrons (neutral)   - Mass Number = Protons + Neutrons   - Neutrons = Mass Number - Atomic Number

Understanding and Calculating Atomic Mass

• Measured in amu; weighted average of isotopes.

• Calculation example for atomic mass based on isotope abundance.