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Transcript
Chapter 4 History of Atomic Theory and Structure https://youtu.be/thnDxFdkzZs Democritis (460-370 BC) First to say that matter is not infinitely divisible Ideas ▪ Atoms are tiny, solid, homogenous, indestructible, and indivisible ▪ Different kinds of atoms have different sizes and shapes ▪ Size, shape, and movements of atoms determines the properties of matter ▪ Matter is made of atoms, which move through empty space Couldn’t explain how atoms were held together Aristotle (384-322 BC) One of Democritus’s biggest critics Rejected Democritus’s theory because it didn’t fit with his own understanding of nature Ideas ▪ Empty space cannot exist ▪ Matter is made of earth, fire, air, and water Influence was so great that the theory of atoms was rejected by everyone for almost 2000 years! John Dalton (1766-1844) Ideas (Dalton’s Atomic Theory) ▪ ▪ ▪ ▪ All matter is made up of atoms Atoms are indivisible and indestructible Atoms of an element are identical Atoms of one element are different from those of another element ▪ Unlike atoms combine in simple whole-number ratios to form compounds ▪ In a reaction, atoms are separated, combined or rearranged ▪ Law of Conservation of Mass: Matter cannot be created or destroyed, only changed in form J.J. Thomson (1856-1940) First person discover a subatomic (smaller than an atom) particle – the electron! Ideas ▪ Atoms are made up of smaller parts ▪ Some parts are negative ▪ Since atoms are neutral, the rest of the atom must be positively charged The Plum Pudding Model (1904) In 1897, Thomson and his team showed that atoms were made up of smaller parts through his experiments with a cathode ray Robert Millikan (1868-1953) Discovered the charge and mass of an electron ▪ Charge is [1-] ▪ Mass is 9.1 x 10-28g or 1/1840 the mass of a hydrogen atom In 1909, Millikan devised the oil-drop experiment and found the charge and mass of an electron Lord Ernest Rutherford (1871-1937) Discovered the nucleus and its positive charge Ideas ▪ Atoms are mostly empty space ▪ There is a positively charged nucleus at the center of the atom made up of protons ▪ The negatively charged electrons orbit the positively charged nucleus randomly The Planetary Model (1911) Alpha particles (α) are fired at an extremely thin sheet of gold Most α-particles passed through, but some were deflected Niels Bohr (1885-1962) Studied the behavior of electrons and discovered electron shells Ideas ▪ Electrons orbit the nucleus in fixed, circular orbits ▪ The paths for these orbits are the same distance away from the nucleus for every kind of element ▪ Electrons can move back and forth from one shell to the next shell He discovered his model by measuring the frequency of light given off by energized particles The Shell Model Louis de Broglie (1892-1987) Predicted that matter (especially electrons) could behave like particles and waves Werner Heisenberg (1901-1976) Formed a new model of the atom using quantum mechanics Heisenberg’s Uncertainty Principle ▪ Determined it is impossible to know both the momentum and location of an object simultaneously Erwin Schrödinger (1887-1961) Formed a new model of the atom using de Broglie’s wave model In 1926-27, Heisenberg and Schrödinger, working independently, came up with new, similar models for the atom James Chadwick (1891-1974) Discovered the neutron, which helped explain isotopes’ different masses Decided the unit of measurement of atomic weight was the atomic mass unit or amu Developed in 1932, the atomic model finally includes neutrons! Thomson Millikan Rutherford Bohr de Broglie Heisenberg Schrödinger Chadwick 1909 1911 1913 1923 1927 1926 1932 Democritus Dalton 1897 ~400 BC 1808