Atomic Theory



460 BC

Greek philosopher remembered mostly for his idea of an atomic theory of the universe. His experiment was taking a seashell and breaking it apart until he had a fine powder. After not being able to break a piece of the powder, he determined he had the atom, the indivisible building block of everything.

Antoine Lavoisier


French chemist who came up with the Law of Conservation of Mass. Conducted experiments transforming elements.

John Dalton


English chemist who developed the law of multiple proportions which talked about how elements combine.

Law of Conservation of Mass


Law by Lavoisier stating in a chemical reaction, matter is neither created nor destroyed. Was discovered while doing chemical reactions, the weight didn’t change.

Dalton’s Atomic Theory


Atomic theory proposed by Dalton. It states that all matter is made of atoms that are indivisible and indestructible, all atoms of a given element are identical in mass and property, compounds are formed by the combination of two or more atoms of different kinds, and a chemical reaction is a rearrangement of atoms.

Dmitri Mendeleev


Russian chemist who created the first periodic table. He arranged his table by properties of the elements.

J.J. Thomson


English physicist who discovered the electron with an experiment that produced cathode rays by introducing gas into a region between charged plates. Thomson tried to prove the rays were electrons.

Ernest Rutherford


New Zealand physicist who conducted the Gold Foil experiment. His experiment allowed him to create the Rutherford model of the atom that introduced the nucleus.

Niels Bohr


Danish physicist who proposed the Bohr model of the atom. Also helped develop the atomic bomb.

Erwin Schrodinger


Austrian physicist who proposed the Quantum Mechanical model of the atom. He used equations to predict the location of electrons in atoms.

Henry Moseley


English physicist who repositioned the periodic table. He arranged it based on atomic weight rather than properties.

Cathode Ray Tube


Tube used by Thomson in the Cathode Ray experiment. It was a vacuum with two electric plates that produced a positive anode and a negative cathode to deflect rays.

Plum Pudding Atomic Model


Model of the atom proposed by JJ Thomson. Proposed that the atom was a positively charged sphere that had negatively charged electrons embedded in it, balancing the total charge.

Gold Foil Experiment


Experiment conducted by Rutherford that proved the existence of a small massive center to atoms. This center became known as the nucleus.

Rutherford Model


Model of the atom proposed by Rutherford. It disputed the plum pudding model of the atom. It introduced the nucleus of the atom which was said to contain the bulk of the atomic mass and have a small volume compared to the rest of the atom.

Robert Millikan


American physicist who measured the charge of electrons. He did this in the oil drop experiment where he dropped oil between electrodes and measured the force of the drops.

Bohr Planetary Model


Model of the atom proposed by Bohr and Rutherford. It proposes that the atom has a small positive nucleus with electrons orbiting the nucleus in a circle, like planets around the sun.

Electron Cloud Model


Model of the atom proposed by Schrodinger. It proposed that rather than electrons moving in orbits like the Bohr model proposed, electrons moved in random places within an electron cloud.

Quantum Mechanical Model


Model of the atom proposed by Schrodinger. It was an improved version of the Bohr model that used equations to predict the likelihood of finding an electron in a certain place.

James Chadwick


English physicist who conducted an experiment bombarding Beryllium with alpha particles. The result was a very energetic stream of radiation. These rays were very penetrating and neutral. The rays knocked protons loose and allowed for the neutron particle to be seen.