History of the ATOM Once Upon a Time …

Democritus Democritus of Abdera Greek Philosopher 400BC “Atomos” compose the world. Tiny, indivisible particles that retain the chemical identity of an element Model of the atom                            

Dalton John Dalton English School Teacher (began teaching at 15!!!) 1766-1844 Atomic Theory of Matter (on Next Slide) Model of atom

Dalton’s 5 Postulates - Atomic Theory of Matter All matter is composed of extremely small particle called atoms. All atoms of a given element are identical and are different from those of any other element. Atoms cannot be created, divided into smaller particles, or destroyed. Different atoms combine in simple whole number ratios to form compounds. In a chemical reaction, atoms are separated, combined or rearranged.

Dalton’s Influences Meteorological Studies (Weather) Democritus Kept daily recordings of weather for 57 years Democritus Robert BOYLE (Irish chemist 1627-1691) Jacque CHARLES Joseph GAY-LUSSAC

Law of Definite Proportions states that a chemical compound always contains exactly the same proportion of elements by mass. Example: Water’s mass ratio is always the same. H2O is

Law of Multiple Proportions The law states that when chemical elements combine, they do so in a ratio of small whole numbers. For example, carbon and oxygen react to form carbon monoxide (CO) or carbon dioxide (CO2), but not CO1.3.

Thompson J.J. Thompson (Joseph John) English Physicist 1856-1940 Electrons – negative sub-atomic particle “plum-pudding” model Cathode-ray Tube Experiment http://www.kentchemistry.com/moviesfiles/Units/AtomicStructure/JJThompson.htm Model Thompson + - + - + - Positive and Negatively charged particles Scattered around (must be electrically neutral)

Rutherford Ernest Rutherford New Zealand Scientist 1871- 1937 Discovered the Nucleus and determined that it has mass and a Positive charge Gold-Foil Experiment Model - http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf http://micro.magnet.fsu.edu/electromag/java/rutherford/

Chadwick James Chadwick English physicist 1891-1974 Neutron – the neutral sub-atomic particle Model of Atom -

Bohr Neils Bohr Danish Physicist 1885 – 1962 Quantized the energy levels electrons could exist in an atom Model of the atom -

Current Model of the Atom Many people Still on-going Electron Cloud Model Model of Atom -