General Chemistry Unit 2 Flashcards

Democritus

Proposed that all matter is made of tiny, indivisible particles called atoms. This was an early atomic idea, but he had no experimental proof.

John Dalton

Developed the first modern atomic theory. Proposed that matter consists of atoms and that atoms of different elements differ. His model pictured atoms as solid spheres.

William Crookes

Used the Crookes tube to study cathode rays, helping advance research into particles inside atoms.

J. J. Thomson

Discovered the negatively charged electron through cathode ray experiments. Proposed the plum pudding model, in which electrons were embedded in a positively charged sphere.

Robert Millikan

Used the oil-drop experiment to determine the charge of the electron, building on the discovery of the electron.

Eugen Goldstein

Observed positively charged canal rays in gas discharge tubes. His work contributed to the study of positive particles, but he did not discover the proton.

Henri Becquerel

Discovered natural radioactivity when uranium salts exposed photographic plates without sunlight. Showed that atoms could emit radiation spontaneously.

Ernest Rutherford

Used the gold foil experiment to show that most of the atom is empty space and that it contains a small, dense, positively charged nucleus. Disproved the plum pudding model.

Niels Bohr

Proposed that electrons occupy specific, quantized energy levels around the nucleus. Explained hydrogen's line spectrum using electron transitions between energy levels.

Max Planck

Proposed that energy is emitted or absorbed in discrete packets called quanta. Helped establish quantum theory.

Albert Einstein

Explained the photoelectric effect by proposing that light transfers energy in packets called photons. Supported the idea that light energy is quantized.

Louis de Broglie

Proposed that particles such as electrons have wave-like properties, introducing the idea of matter waves.

Erwin Schrödinger

Developed a wave equation used to describe electron behavior. His model describes the probability of finding electrons in orbitals rather than fixed paths.

Werner Heisenberg

Developed the uncertainty principle: the exact position and momentum of an electron cannot both be known precisely at the same time.