-
415 BCE
Democritus
Democritus was the first to come up with atomic theory. Since there wasn’t any advanced scientific tools at the time, all he had was theories. His theory is based off of all matter being made up of atoms. These atoms were solid, invisible, and indestructible. The atoms came in different shapes and sizes. -
John Dalton
John Dalton built off of Democritus atomic theory. He did many experiments with gases. These experiments gave some of the earliest atomic masses. They also led to early concepts of atomic structure and reactivity. His updated atomic theory included that all atoms of a given element are the same. Different elements also had atoms that vary in size and shape when compared to each other. -
J.J. Thompson
J.J. Thompson was the first to discover the electron. He deflected rays off of electrically charged plates and magnets. From his data, he determined that there were bottoms much smaller than the atoms, which was electrons. Thompson also suggested a new model of the atom. This new model was a sphere of positive matter where electrons’s positions were based off of electrostatic forces. -
Ernest Rutherford
Ernest Rutherford postulated the nuclear structure of the atom. He shot alpha particles at gold foil. Most passed through, while others slightly deflected or completely deflected. This experiment showed that the atom contain mostly empty space. It also showed that there was a dense positively charged center of the atom, the nucleus. -
Niels Bohr
Niels Bohr’s greatest contribution was the atomic model. This model showed the atom as a small ,positively charged nucleus surrounded by electrons. He also discovered that electrons had separate orbits around the nucleus. He also found that the number of electrons determined the properties of a element.
