Robert Millikan's primary contribution to atomic theory came as a result of his oil-drop experiment, which measured an electron's charge. Previously, J.J. Thomson had suggested the hypothesis that an electron's mass was at least 1,000 times less than the mass of the tiniest atom. Millikan's contribution to this hypothesis was to specify the size of the electron's charge.Know More
Millikan's oil-drop experiment involved spraying oil from a perfume atomizer into a sample chamber. Some of the droplets traveled through a pinhole into a space between two plates, one of which had a negative electric charge and the other of which had a positive charge. This central chamber was then ionized with X-rays. Particles that failed to catch electrons followed gravity to the bottom plate, while particles that managed to catch at least one electron floated up to the positive plate or fell at a slower rate of speed. Millikan reached the conclusion that each drop had a charge that was a multiple of 1.59 x 10^(-19) Coulombs.
Later, Millikan also verified Albert Einstein's photoelectric equation and developed the first photoelectric calculation of Planck's constant h. Later studies involved hot-spark spectroscopy of the various elements, pushing the ultraviolet spectrum far past the known lowest limit, and his motion law for a particle falling earthward after coming into the atmosphere, which led to his radiation studies.Learn more about Atoms & Molecules
Dalton's atomic theory states four critical truths about atoms: firstly, everything is made up of atoms and atoms cannot be destroyed. Secondly, all atoms within a single element are identical. Thirdly, compounds are formed from two or more different kinds of atoms. Finally, chemical reactions rearrange atoms.Full Answer >
In 1905, Albert Einstein published an analysis in which he devised a mathematical way to predict the size of both atoms and molecules. At the time, the science of atoms was still in its infancy, but Einstein's test was crucial in leading the way towards testing the reality of atoms.Full Answer >
The atomic theory formulated by the British chemist John Dalton proposes that atoms are indivisible particles comprising all matter; atoms of the same element share identical properties, including shape, size and mass; atoms of an element are unique and vary from the atoms of different elements; atoms are the fundamental units of a chemical reaction; atoms are conserved and can neither be created nor destroyed; and atoms combine in simple, fixed proportions to produce compound atoms, known as molecules. Dalton is commonly referred to as the father of the modern atomic theory.Full Answer >
Democritus, an ancient Greek philosopher, was not the first to propose an atomic theory, as his mentor Leucippus originally proposed it. Democritus adopted the theory, developed it further, and provided a more detailed and systematic view of the physical world.Full Answer >