Origins of the Atomic TheoryPhysical Science2009-2010psquires
The Development of the Atomic Theory♦Democritus and Dalton:♦atomic theory
Democritus♦Greek philosopher ~ 300 BC♦Limit to “smallness”♦All matter consists of tiny, indestructible particles called atoms♦Atomos – indestructible
John Dalton First serious atomic theory♦English scientist♦Studied the properties of gases♦“Reinvented” the idea of atoms♦Published in 1803
Dalton’s atomic theory - 1803 1. Elements are composed of tiny, discrete, particles called atoms.
Dalton’s atomic theory - 18032. Atoms are indivisibleand indestructible and donot change their identityduring reactions.
Dalton’s atomic theory - 18033. Atoms of the sameelement are identical inmass and chemical andphysical properties. Atomsof different elements aredifferent.
Dalton’s atomic theory - 18034. Atoms combine to formcompounds in simple,whole-number ratios.Law of Definite Proportions
Dalton’s atomic theory - 18035. Atoms combine indifferent ratios to maketwo or more compounds.Law of Multiple Proportions
The Development of theAtomic Theory♦Thomson: CRT’s and the electron
J. J. Thomson♦Cathode rays - cathode ray tube♦Attracted to positive electrode♦Thought they might be atoms♦Had same charge to mass ratio regardless of metal in the cathode♦Particle must be common to all matter, a subatomic particle
Cathode Ray TubeIt was also used by J. J. Thomson Cathode Anode High voltage +
That particle was called the … TheThe electron electron The Electron The electronThe electron Discovered in 1897 The electron By J. J. Thompson
J. J. ThomsonIf that were the case, then theelectron would be much smallerthan the smallest atom, … showing for the first time that matter is made up of particles smaller than atoms.Thomson tried to measure thefundamental charge on the electron.
The Development of theAtomic Theory♦Rutherford: “Gold Foil Experiment”
Rutherford’s Nuclear AtomAlpha particles were repelled by…… a small, dense, positivelycharged nucleus. Almost all the mass of an atom is in the nucleus.Electrons are located outside thenucleus.
Niels Bohr♦ Electrons travel in fixed orbits around the atom’s nucleus.♦ Bohr also described the way atoms emit radiation by suggesting that when an electron jumps from an outer orbit to an inner one, that it emits light.♦ Later other physicists expanded his theory into quantum mechanics.♦ This theory explains the structure and actions of complex atoms.