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Chapter 4 Sections 1 and 2 Atomic History and Structure Of the 11 key scientists discussed, which do you believe had the most important contribution? Why? L. Bernard, 2015 Do Now • Smallest particle of an element • All matter is created of atoms • Comes from the Greek word atomos • “indivisible” L. Bernard, 2015 The Atom • Greek philosopher • First to propose the idea of the atom’s existence • Theorized that the atom is indivisible and indestructible, but had no experimental evidence L. Bernard, 2015 Democritus (460 – 370 B.C.E.) • English chemist and teacher • Pioneered the modern discovery process about atoms • Transformed Democritus’s theories on atoms into an actual scientific theory L. Bernard, 2015 John Dalton (1766-1844) Dalton’s Atomic Theory 1. All elements are made up of atoms, which are small invisible particles 2. Atoms of the same element are identical 3. Atoms of different elements can chemically combine in whole-number ratios to form compounds 4. Chemical reactions occur when atoms are separated, joined together, or rearranged; but atoms cannot change into another element because of a reaction L. Bernard, 2015 Published 1808 • Studied the way elements combined in chemical reactions and the ratio in which they combined • Ex: Liquid mercury • All drops have the same properties • All drops are made of the same atoms L. Bernard, 2015 How did Dalton create his theory? • Mostly! • However atoms are now known to be divisible • They are comprised of smaller subatomic particles known as protons, neutrons, and electrons L. Bernard, 2015 Is Dalton’s theory accepted today? • A Russian chemist and teacher • Arranged the then 60 known elements in order by increasing atomic mass • Created the first periodic table in 1869 L. Bernard, 2015 Dmitri Mendeleev • Discovered the electron in 1897 • Passed electric current through a tube filled with gas and observed a glowing beam known as a cathode ray • Concluded all atoms contained electrons L. Bernard, 2015 J. J. Thomson (1856-1940) L. Bernard, 2015 Cathode Ray • Electrons pass from the negatively charged cathode to the positively charged anode • Created a glowing beam of light • Proved that negative particles (electrons!) were being attracted to the positive anode • Thomson believed electrons were evenly distributed throughout the atom • The atom was also filled with positively charged material • This model was later disproved L. Bernard, 2015 “Plum-Pudding Model” of the Atom • U.S. Physicist • Calculated the charge of an electron in 1909 • 1.60 x 10-19 Coulomb • Also calculated the mass of the electron • 1/1840 the mass of a hydrogen atom L. Bernard, 2015 Robert A Milikan (1868-1953) • Discovered positively charged subatomic particles called protons in 1886 • Used a variation of the cathode ray • Calculated the mass of the proton • 1840 times the mass of the electron L. Bernard, 2015 Eugen Goldstein (1850-1930) • Confirmed the existence of neutrally charged particles, the neutron, in 1932 • Calculated that neutrons had a mass equal to the mass of a proton L. Bernard, 2015 James Chadwick (1891-1974) How do we describe the structure of the atom? L. Bernard, 2015 • Atoms are made of protons, neutrons, and electrons • How are they put together to make an atom? • Former student of J. J. Thomson • Devised the gold-foil experiment in 1911 • Created a new atomic model based on his findings L. Bernard, 2015 Ernest Rutherford (1871-1937) L. Bernard, 2015 Gold Foil Experiment • Alpha particles (Helium atoms without two electrons) were shot at a sheet of gold foil • Some particles passed through the foil but a few were deflected • Why?? L. Bernard, 2015 The nuclei of the gold atoms in the foil deflects the small alpha particles; the empty space surrounding the nuclei lets other alpha particles pass through. • The atom is mostly empty space • All the positive charge and almost all the mass of the atom is contained in the nucleus • The nucleus is made of the protons and neutrons • Electrons are distributed around the nucleus • Electrons occupy almost all of the atoms volume • Rutherford’s model is still being revised today! L. Bernard, 2015 The Rutherford Atomic Model • Danish student of Rutherford • In 1913 he proposed that an electron is found only in specific circular paths known as orbits around the nucleus L. Bernard, 2015 Niels Bohr (1885-1962) L. Bernard, 2015 The Bohr Model • French Physicist • In 1923, he proposed that all moving particles, including electrons, had properties of waves • Influenced Schrödinger's work L. Bernard, 2015 Louis de Broglie (1892 – 1987) • Austrian physicist • Devised and solved a mathematical equation to describe the true behavior of electrons in atoms in 1926 • Known as the quantum mechanical model L. Bernard, 2015 Erwin Schrödinger (1887-1961) L. Bernard, 2015 Modern Day Model of the Atom Scientist Pamphlet Project! • • • • • Where they were born/where they lived Family life How they got interested in science Any other discoveries they may have made Prizes, awards, honors, and recognitions they got before and after death • Any fun facts! • Make sure that your information and drawings cover the entire pamphlet! L. Bernard, 2015 • Choose one of the 11 key scientists you researched today to create a pamphlet on • Do further research and include lots of information on your chosen scientist such as