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Period: 300 to
Atomic Theory Assignment 1
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John Dalton
His experiments showed that the known elements combined in His experiments showed that the known elements combined in definite and constant proportionsHe hypothesized that the elements must be made of smaller pieces of matter; he called these atomsMade the idea of atoms “useful” -
Dmitri Mendeleev
Arranged elements into 7 groups with similar properties. He discovered that the properties of elements "were periodic functions of the their atomic weights". This became known as the Periodic Law. -
J.J. Thomson
Stated that atoms were not simple solid spheresHe discovered electrons which are small particles located on the outside of the nucleus and have a negative chargeThis discovery answered the question of why the needle in a compass always points north -
Ernest Rutherford
Designed an experiment where he fired a stream of charged particles at a thin sheet of gold foil; he observed how most of the particles passed through the gold foil.This allowed him to conclude that atoms are made mostly of empty spaceHe called the positively charged center of an atom the nucleusSaid positively charge particles where in the nucleus, and negatively charged particles where on the outside, around the nucleus -
Robery Millikan
Discovered the negative charge carried by electrons using his oil-drop method in 1910He preformed this by determining the charge of oil drops when held at equilibrium.He measured the density, mass, and radii of the oil drops and he calculated the gravitational and buoyant forces in order to find the charge -
Niels Bohr
Proposed that electrons orbit around the nucleusStated that each electron has a fixed amount of energyAlso that electrons orbit in energy levels forming rings around the nucleusThe energy climbing up and down a ladder gives you a great understanding of this concept and how electrons can move throughout energy levels -
Sir James Chadwick
Chadwick’s most famous discovery was of the neutron in 1932.This led to the fissioning of Uranium-235, and therefore the atomic bombHe observed that, if exposed to assault of alpha particles, beryllium released unknown radiation that ejected protons from nuclei of substances.The discovery also refuted previous ideas that the extra mass in the nucleus was protons paired with electrons (this would supposedly make it neutral). -
Democritus and Leucippus
Contributed to the ancient atomic theoryDid not accept the Eleatic hypothesis that said "everything is one.”So they dug deeper, and discovered that the world essentially consists of myriads of tiny indivisible particles, which they called atoms.
