Chemistry Unit 3: Atomic Structure

John Dalton's Atomic Contribution

Proposed solid sphere model and atomic theory; 1803.

JJ Thomson's Atomic Contribution

Discovered the electron using a cathode ray tube; 1897.

Ernest Rutherford's Atomic Contribution

Discovered the nucleus via gold foil experiment; 1911.

Niels Bohr's Atomic Contribution

Proposed planetary model with quantized orbits; 1913.

Erwin Schrödinger's Atomic Contribution

Proposed quantum mechanical model using wave equations; 1926.

Proton

Positive charge (+1), ~1 amu, found in nucleus.

Neutron

Neutral charge (0), ~1 amu, found in nucleus.

Electron

Negative charge (-1), ~0 amu, found in electron cloud.

Conservation of Mass

Mass is neither created nor destroyed in a chemical reaction.

Law of Multiple Proportions

Elements can combine in ratios of small whole numbers.

Cathode Ray Tube

Vacuum tube emitting a beam of electrons, used by Thomson.

Plum Pudding Model

Thomson's model: electrons scattered in a positive 'soup'.

Gold Foil Experiment

Rutherford: alpha particles fired at gold foil; proved dense nucleus exists.

Alpha Particle

Helium nucleus (2 protons, 2 neutrons) emitted by radioactive decay.

Nucleus

Dense central core of an atom containing protons and neutrons.

Neutron Star

Extremely dense remnant of a collapsed giant star composed mostly of neutrons.

Isotope

Atoms of the same element with different numbers of neutrons.

Atomic Mass

The weighted average mass of an element's isotopes.

Spectroscope & Emission Spectrum

Device splitting light into specific wavelengths emitted by excited atoms.

Double Slit Experiment

Light acts like waves, overlapping to create a striped pattern when passing through two narrow openings.

Satellite/Planetary Model

Bohr model: electrons orbit the nucleus like planets around the sun.

Energy Level

Fixed regions around a nucleus where electrons can exist.

Orbital

3D region around a nucleus with a high probability of finding an electron.

Excited and Ground State

Ground is lowest energy state; excited is higher energy state.

Wavelength of Light Relationship

Shorter wavelength = higher energy and frequency (e.g., blue/violet).

Prism & Diffraction Grating

Tools that separate light into its component wavelengths/colors.

Electron Configuration

An address showing where electrons are housed in the atom.