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Early atomic theory • The Greek philosophers (400 BC) –Democritus –Aristotle 9 “New” atomic theory • John Dalton (early 1800 1800’s) s) –Proposed first atomic theory b k d with backed h experimentall evidence. 10 “New” atomic theory • John Dalton (early 1800 1800’s) s) –Studied the work of Antoine Lavoisier and Joseph Proust –Lavoisier – law of conservation of mass –Proust – law of definite proportions (ratio of masses) 11 “New” atomic theory • John Dalton (early 1800 1800’s) s) –Proposed the law of multiple proportions –Explained Explained a few years later by Amadeo Avagadro 12 Dalton’s atomic theory • John Dalton (early 1800 1800’s) s) –All matter is composed of atoms, which h h are the h smallest ll possible bl p particle. 13 Dalton’s atomic theory • John Dalton (early 1800 1800’s) s) –All atoms of the same element are identical. d l 14 Dalton’s atomic theory • John Dalton (early 1800 1800’s) s) –Atoms combine in simple whole number b ratios. 15 “New” atomic theory • Dalton’s Dalton s work –Since been tested and proved correct –As As new discoveries happened, major revisions have occurred. 16 Modern atomic theory •J J.J. J Thomson (1897) –Cathode ray tube –Discovered Di d th the electron l t –Changed g gas g in tube and concluded all contained the p particle 17 Modern atomic theory 18 Modern atomic theory •J J.J. J Thomson (1897) –Calculated the charge to mass ratio of f an electron l –Won Won the Nobel Prize in Physics in 1906 for his work. 22 Modern atomic theory • Robert Millikan (1916) –Performed the oil drop experiment –Discovered Discovered the actual mass of an electron, then the charge using Thomson’ss work. Thomson work 23 Modern atomic theory 24 Modern atomic theory • Robert Millikan (1916) –Won the Nobel Prize in Physics in 1923 for f h his work k 25 Modern atomic theory • Since the atom has a negative particle, it was not a big leap to conclude it must have a positive one as well. • Why? 26 Modern atomic theory • Ernest Goldstein (1897) –Discovered the proton 27 Modern atomic theory • The proton and electron were found to have an identical charge, only opposite pp sit in sign. si n 28 Modern atomic theory • A third particle would go undiscovered for some time, although lth h it wass predicted p di t d to t exist xist by Lord Rutherford in 1920. 29 Modern atomic theory • James Chadwick (1932) –Discovered the neutron –It is equal in mass to a proton, but has no charge 30 Modern atomic theory • These discoveries lead us to the first major revision to Dalton’s atomic t mi th theory. 31 Modern atomic theory • Dalton stated that atoms are the smallest possible particle. Not true! • They are made up of protons, protons neutrons, and electrons. 32 Modern atomic theory • These newly discovered particles are called sub-atomic particles. 33 Models of the atom • Once these sub-atomic particles had been discovered, scientists st t d tto wonder started nd h how they th fit together. 34 The atom • More on this later… later • Some more facts about atoms… 35 The atom • While working with Neon, Neon Thomson found two kinds of Neon atoms. Th were alike They lik chemically, h mi ll but b t had h d different masses. 36 The atom • We now know these are called isotopes. • Isotopes are atoms of f the h same element with different masses. 37 The atom • By the mid-1800 mid-1800’ss, about 70 elements had been discovered and s i ntists were llooking scientists kin f for a way tto organize them. 39 The atom • Dimitri Mendeleev –Known as the father of the periodic table –Arrange his table according to atomic t i mass –Left blank spaces p for undiscovered elements 40 The atom • Dimitri Mendeleev –Problems- Co and Ni, Te and I, Ar and dK 41 The atom • Henry Moseley (1913) –Studied the x-rays produced by d ff different metals l in an x-ray tube b –Discovered Discovered atomic number 42 The atom • Atomic number is the number of protons in an atom’s nucleus. • It determines d the h identity d of f an element. 43 The atom • The periodic table is organized according to increasing atomic n mb number. periodic law. • Called the p 44 The atom • Another revision to Dalton’s Dalton s atomic theory: • Atoms of one element contain the same number of protons, but can contain different numbers of neutrons. • Isotopes! I t ! 45 Isotopes • Another name for an isotope is a nuclide. • Nucleons are particles that make up the nucleus. • Mass M number b is i the th number b of f nucleons. 46 I t Isotope # # Atomic of f of f # p+ e - # Mass of f # 0 n Lithium-8 92 238 19 22 8 18 47 I t Isotope # # Atomic of f of f # p+ e 11 # Mass of f # 0 n 14 92 235 98 T 43 Tc 87 136 49 I t Isotope # # # Atomic Mass of f of f of f # # + 0 p e n 8 14 79 102 238 T Tc 81 136 51 Models of the atom • Now scientist began to wonder how do these protons, electrons, and n t ns fit ttogether. neutrons th 52 Dalton (1803) • Remember Dalton believed atoms were indivisible. So his model was a s lid sph solid sphere. 53 Dalton 54 J.J. Thomson (1897) • Thomson discovered the electron, electron so he amended Dalton’s model to in l d th include the electrons. l t ns 55 J.J. Thomson (1897) • It is called the plum-pudding model model. • Better analogy- like raisins stuck on the h surface f of fab ball ll of f dough. d h 56 Models of the atom 57 Rutherford (1909) • Performed the gold foil experiment. experiment 58 Rutherford (1909) 59 Predicted to happen 60 Actually happened 61 Rutherford’s quote • ” It was about as credible as if you had fired a 15-inch artillery shell at a piece pi of f tissue tiss paper, p p and nd it came m back and hit you.” 62 Rutherford • The two major finding of Rutherford through the gold foil experiment: 1. The atom is mostly empty space 2 It contains 2. t i a positively iti l charged h d nucleus. 64 Rutherford 65 Bohr (1913) • Neils Bohr was a student of Rutherford’s. He proposed the pl n t planetary model. m d l It st states t s th thatt the electrons revolve around the nucleus l in set orbits. 66 Bohr (1913) • These orbits can be viewed like the rungs of a ladder. • The h electron l can move from f one orbit to another, but cannot exist in between orbits. 67 Bohr (1913) • This is a statement of the quantum theory, the idea that not all ll values l s of f energy n exist, xist only nl certain values. 68 Bohr (1913) • The rungs of the “ladder” ladder are not equally spaced. • The Th f farther th from f the th nucleus, l the closer the rungs are to each other, th the th less l energy needed d d to t jump to the next level. 69 Bohr (1913) 70 Schrodinger (1926) • Schrodinger took Bohr Bohr’ss model one step farther. • He used the newly developing quantum theory to wr write te mathematical equations to explain all possible locations of the electron in a hydrogen atom. 71 Schrodinger (1926) • His model was quantized, quantized like Bohr’s model, but the orbits were not as defined. defined • His equation could be solved for all ll probable b bl llocations ti f for an electron. 72 Schrodinger (1926) • These probable locations would give an electron density di ib i resulting distribution l i iin an electron cloud. • The darker the cloud, the more probable the location. location 73 Schrodinger (1926) • It is called the quantum mechanical model, or electron cloud l d model. d l • This h s iss still st ll accepted today. 74 Schrodinger (1926) 75