AP Chem Scientists to Know

Democritus

Proposed that all matter is made of tiny, indivisible particles called atoms (“atomos” = uncuttable). Believed atoms differ in size, shape, and motion, forming all substances

Dalton

Developed Atomic Theory:
All matter is made of atoms, atoms of the same element are identical, atoms combine in whole # ratios to form compounds, chemical rxns rearrange atoms, not create/destroy them.

Created the first modern atomic model based on experimental evidence.

Franklin

Discovered positive and negative electrical charges. His studies of electricity laid groundwork for understanding charged particles in atoms.

Crookes

Invented the [his name] tube (cathode ray tube). Discovered cathode rays, showing that atoms contain smaller charged particles.

Thomson

Used the cathode ray tube to discover the electron. Proposed the “plum pudding model”: electrons embedded in a positively charged sphere. Measured the charge-to-mass ratio (e/m) of the electron.

Millikan

Conducted the oil drop experiment. Determined the charge and mass of the electron.

Goldstein

Discovered canal rays (positive rays) in cathode ray tubes. Credited with discovering the proton (positive particle).

Roentgen

Discovered X-rays while experimenting with cathode rays. Won the first Nobel Prize in Physics (1901).

Becquerel

Discovered radioactivity using uranium salts. Found that certain materials emit radiation without external energy.

Rutherford

Conducted the gold foil experiment. Discovered the nucleus and proposed that atoms are mostly empty space. Later discovered the proton (1919). Proposed the nuclear model of the atom.

Chadwick

Discovered the neutron, completing the modern picture of the atom.

Moseley

Determined that atomic number (number of protons) defines the element, not atomic mass. Created the modern periodic table ordering by atomic number.

Balmer

Found the [this name] series — a mathematical formula describing the visible spectral lines of hydrogen. Helped establish the link between spectra and atomic structure.

Planck

Founded quantum theory. Proposed that energy is emitted in discrete packets called quanta (E = hf).

Bohr

Developed the [this name] model of the atom. Proposed that electrons orbit the nucleus in specific energy levels and emit/absorb photons when changing levels.

Einstein

Explained the photoelectric effect, showing light behaves as particles (photons). His work supported Planck’s quantum theory. [Equation: E=hf]

DeBroglie

Proposed wave-particle duality — all matter has wave properties. Introduced the de Broglie wavelength [Formula: λ=h/mv]

Heisenberg

Formulated the Uncertainty Principle: It is impossible to know both the position and momentum of an electron simultaneously.

Schrodinger

Developed the wave equation for quantum mechanics.

Described electrons as wave functions (probability clouds) rather than fixed orbits. Created the quantum mechanical model of the atom.