Chem-History of Atoms

Atom

Smallest particle retaining element's properties.

Democritus

First to propose indivisible particles, 'atomos'.

Antoine Lavoisier

Father of Modern Chemistry; mass conservation principle.

John Dalton

Developed atomic theory using experimental methods.

Dalton's Atomic Theory

Five postulates explaining atomic behavior and interactions.

Atom Size

Atoms range from 30 to 300 trillionths of a meter.

Subatomic Particles

Protons, neutrons, and electrons make up atoms.

J.J. Thompson

Discovered electrons via cathode ray experiments.

Cathode Ray

Glowing beam traveling from cathode to anode.

Plum Pudding Model

Thompson's model of atom with embedded electrons.

Robert Millikan

Calculated electron charge using oil drop experiment.

Ernest Rutherford

Proposed nuclear model after gold foil experiment.

Gold Foil Experiment

Showed atom has a dense nucleus with protons.

Neils Bohr

Proposed electrons travel in defined orbits.

Bohr Model

Electrons exist in specific energy levels around nucleus.

James Chadwick

Discovered neutron, increasing atomic mass without charge.

Atomic Number

Number of protons in an atom's nucleus.

Atomic Mass

Total mass of protons and neutrons in atom.

Isotopes

Atoms of the same element with different neutrons.

Atomic Mass Units (amu)

Unit for measuring atomic mass of particles.

Weighted Atomic Mass

Average mass considering natural isotope abundance.

Chlorine Isotopes

Chlorine-35 and chlorine-37 with different abundances.

Chemical Reactions

Atoms rearranged; elements do not change types.

Energy Levels

Fixed distances where electrons orbit nucleus.

Scanning Electron Microscope

Device for visualizing atoms at high resolution.

Nucleus

Core of atom containing protons and neutrons.