What is the Structure of the Atom? Over 2,400 years ago, Greek philosophers understood that matter must consist of a small, single unit. The Greeks called the basic unit of matter, ‘atomos’ meaning indivisible or cannot be broken smaller. We must look back in history to scientists’ quest for knowledge and understanding.

Early Discoveries Scientists That Studied the Structure of the Atom: Dalton Crookes Thomsom Becquerel Rutherford Chadwick Niels Bohr

John Dalton In 1802, John Dalton, a British chemist, developed the first model of the atom. Dalton’s atom was a solid, indivisible particle. Developed the first atomic theory.

William Crookes British physicist. In the late 1800’s, created a vacuum tube with a positive and negative terminal. This tube, later known as a cathode ray tube, was used for experiments.

J. J. Thompson Experimented with Crookes’s vacuum tube. Observed the beam of particles bent in the presence of an electric field. Showed the particles had less mass than an atom. Received the Nobel Prize in 1906 for his discovery of the electron. Thompson’s model of the atom resembled a blueberry muffin.

Henri Becquerel Accidentally discovered radiation from a sample of uranium left on a photographic plate. Discovered that atoms of uranium give off negatively charged particles; evidence that atoms were made up of smaller particles. In 1896, Becquerel received the Nobel Prize for the discovery of radiation.

Ernest Rutherford After Becquerel’s discovery of radiation, Rutherford further studied individual particles; alpha, beta and the gamma ray. His studies gave science more information about the atom and even more questions. In 1908, Rutherford won the Nobel Prize in chemistry concluding the atom had a positively charged nucleus and an electron orbiting.

James Chadwick In 1932, Chadwick, a student of Rutherford’s, studied radiation from beryllium. His particle was not affected by an electric field, therefore it must have had a neutral charge. In 1935, Chadwick won the Nobel Prize for his discovery of the neutron.

Niels Bohr 1885 – 1962 1911 Worked under Sir J.J. Thomson in Cambridge England 1912 Worked in Rutherford’s Laboratory in Manchester England Professor of Theoretical Physics at Copenhagen University Researched the nucleus of the atom; “Neutron Capture” Developed the “Electron Cloud” model of the atom