The History of the ATOM

The History of the ATOM The History of the ATOM Early Chemistry  1000 B.C.- Processed ores for weapons and embalming fluids  400 B.C.- Ancient Greeks Aristotle proposed all matter was made up of 4 elements: FIRE, EARTH, WATER, AIR Democritus  “ATOMOS” – Atoms can’t be cut or divided.  All atoms are small, hard particles.  Atoms are always moving.  Atoms join together to form different materials. The Age of Alchemy Next 2000 years-ALCHEMY-a pseudoscience emerged. People thought they could turn metals into GOLD. Wrong thinking!! Some good Chemistry came from making mistakes, however. Dalton’s Atomic Theory of Matter John Dalton wrote his own theory in 1803.  All substances are made of atoms.  Atoms of the same element are the same, and atoms of different atoms are different.  Atoms join together to form new substances.  During a chemical reaction, atoms are neither created nor destroyed. THE ELECTRON  J.J. Thomson, England, found mistakes in Dalton’s theory.  He discovered negative particles inside the atom.  Experiments using particle beam in a cathode ray tube led to discovery of the negative electron.  “Plum Pudding Model” developed. The Nuclear Atom  Ernest Rutherford, 1809, England, tested Thomson’s “plum pudding model.”  Alpha particles were directed at gold foil.  Particles were deflected and reflected.  Reflected particles encountered a “direct hit” with a dense positive center of atom  A dense core or NUCLEUS contains most of the mass of the atom. Rutherford’s New Model  The atom is mostly empty space where electrons travel.  The atom has a small, dense, positively charged nucleus.  Electrons travel around the nucleus like planets around the sun, but their exact places cannot be described. Niels Bohr: Electrons Can Jump o 1913- Niels Bohr said electrons traveled around the nucleus in definite paths. o He thought that no paths were found between the levels. o Electrons could jump from one level to another. What About Protons and Neutrons?  After the discovery of the nucleus, Rutherford determined to find out why the nucleus was positively charged.  The positive part of the nucleus became the proton, thanks to Rutherford in 1920.  The neutron was much harder to find. In 1932, James Chadwick found the extra mass in the nucleus to be the neutron. The Current Theory  1926-Austrian physicist, Erwin Schrodinger and German physicist, Werner Heisenberg published work to explain the nature of electrons.  Electrons do NOT travel in definite paths.  The exact path of the electron cannot be predicted but is likely to be found in regions called electron clouds.  WOW!! Quarks and Gluons Protons and neutrons are composed of smaller particles called quarks. Murray Gell-Mann and George Zwieg suggested their existence in 1963.  “up”, “down”, “top”, “bottom”, “strange”, and “charm” Gluons “glue” quarks together with the strong nuclear force.