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History of the Atomic Model
Transcript of History of the Atomic Model
describes the motion of electrons and work leads to electron cloud Greek Model History of the Atomic Model Democritus, philosopher
atoms from the Greek word "atmos" which meant "uncut" or "indivisible"
different atoms had different properties
liquids were round and smooth
solids were rough and prickly Dalton's Model John Dalton
Paper describing his model was published in 1805
Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
In chemical reactions, atoms are combined, separated, or rearranged. Rutherford's Model 1911
all of an atom's positive charge is concentrated in the nucleus
Electrons move randomly in the space around the nucleus
Electrons eventually spiral into the nucleus due to gravity Thomson's Model J.J. Thomson
atom is neutral, meaning it has neither a positive or negative charge
negative charges and electrons are scattered in a positively charged mass of matter, "plum pudding" model
negative and positive charges balance out the atom
disproved Dalton's "solid ball" atom and showed atoms are made of even smaller particles Bohr Model 1913
Focused on the electrons
Electrons move in spherical orbits only at certain allowed distances from the nucleus.
Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower-energy orbit.
An atom absorbs energy when an electron gets boosted from a low-energy orbit to a high-energy orbit Wave (Quantum) Model 1924
Prince Louis de Broglie
electrons have some properties like waves 1932
confirms existence of neutrons which have no charge 500 500 1000 1500 2000 B.C. A.D. Dalton Model Thomson Model Rutherford Model Bohr Model Wave Model
1803 John Dalton
no internal structure 1897 J.J. Thompson
"plum pudding" model
sphere composed of positively charged matter
electrons embedded in sphere 1911 Ernest Rutherford
positively charged nucleus
electrons move randomly in space 1913 Niels Bohr
electrons move in spherical orbits at fixed distances from nucleus
electrons gain or lose energy when moving between levels 1926 Erwin Schrodinger
develops equations describing motion
his work leads to cloud/wave model