Atomic Theory History
Atomic History
Democritus: Was the Greek philosopher that developed the idea of atomos- the idea of the world is composed of tiny indivisible and indestructible particles.
John Dalton: one of the first people to try to prove the ideas Democritus presented. Dalton created the first atomic theory that consisted of five main principles.
Elements are composed of tiny, indivisible particles called atoms.
all atoms of an element are identical and physical and chemical properties.
atoms of one element are different from atoms of another element.
Atoms combine in simple whole number ratios to form compounds.
atoms cannot be created, destroyed, or changed.
J.J Thomson: Discovered the electron in the atom- showed that atoms could be divided into smaller pieces. He originally called these particles corpuscles but now we call them electrons. The discovery of the electron came about because of experiments with cathode ray tubes.
The cathode ray is a stream of electrons produced at the negative electrode of a tube containing a gas at low pressure.
The model Thomson developed of the atom was the electrons evenly distributed in a positive mass. It improved Dalton's model and it showed how atoms can be divided.
Robert Millikan: Did the oil drop experiment to determine the charge of electrons.
Ernest Rutherford: Discover the nucleus of the atom and change the model of the atom to the nuclear model where the atom is mostly empty space with a dense nucleus. he discovered the nucleus by doing the gold foil experiment.
Rutherford used alpha particles to test the plum pudding model. The experiment showed most of the particles went through the gold foil but a small amount were deflected.
Niels Bohr: By using the element hydrogen he improved on Rutherford's models of the atom. Using atomic emission spectra, he developed the idea of electrons circling the nucleus of an atom in fixed orbits. These orbits were thought to have fixed energies and so were called energy levels.
Max Planck: Believed energy was quantized. electrons have to absorb whole packages of energy and different packages of energy exist and they relate to different frequencies of light.
E=Hv
Werner Heisenberg: Heisenberg uncertainty principle- can either determine the velocity or the position of an electron, cannot determine both.
Louise de Broglie: Only whole numbers of wavelengths are allowed in a circular orbit of a fixed radius. Light has characteristics of both waves and particles. electrons move in wave-like motion with restricted circular orbits.