VII Atomic Structure and Quantum Theory B

VII Atomic Structure and Quantum Theory B - VII Atomic...

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VII Atomic Structure and Quantum Theory B Atomic Models Quantum Numbers and Bonding
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Atomic Models Thomson Model (Early 1900’s) “plum pudding” model Atoms is cloud of positive charge with nuggets of negative charge embedded in it.
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Atomic Models Rutherford Model (1909) Devised experiment to test Thomson Model Stream of alpha particles ( α ) (He 2+ ) at metal foil - if Thomson correct - expected to pass through with minimum dispersion. But saw major deflection, some even coming right back at the source. Rutherford concluded: 1) mass of atom is concentrated in a small region in the center of the atom (nucleus) and has a positive charge. origin of nuclear atom 2) nucleus surrounded by large void containing electrons moving at random.
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Bohr Model (1913) Was attempting to explain line spectra Used a combination of classical and quantum physics Treated only H atom (one electron system)
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Bohr Model (1913) Assumptions 1) Only certain set of allowable circular orbits for an electron in an atom 2) An electron can only move from one orbit to another. It can not stop in between. So discrete quanta of energy involved in the transition in accord with Planck (E = h ν ) 3) Allowable orbits have unique properties particularly that the angular momentum is quantized. mvr = nh 2 π
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Bohr Model (1913) Equations derived from Bohr’s Assumption Radius of the orbit r 1 r 2 r 3 n=1 n=2 n=3 r n = n 2 a o Z a o = h 2 4 π 2 me 2 n = orbit number Z = atomic number h = Planck’s constant m = mass of electron e = charge on electron
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Bohr Model (1913) For H: For He + (also 1 electron) r 1 = 1 2 a o 1 = a o Called Bohr radius r 2 = 2 2 a o 1 = 4 a o r 1 = 1 2 a o 2 = 1 2 a o Smaller value for the radius. This makes sense because of the larger charge in the center For H and any 1 electron system: n = 1 called ground state n = 2 called first excited state n = 3 called second excited state etc.
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Bohr Model (1913) Which of the following has the smallest radius? A) First excited state of H B) Second excited state of He + C) First excited state of Li +2 D) Ground state of Li +2 E) Second excited state of H
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Bohr Model (1913) Which of the following has the smallest radius? A) First excited state of H B) Second excited state of He + C) First excited state of Li +2 D) Ground state of Li +2 E) Second excited state of H r 2 = 2 2 a o 1 = 4 a o r 3 = 3 2 a o 2 = 9 2 a o r 2 = 2 2 a o 3 = 4 3 a o r 1 = 1 2 a o 3 = 1 3 a o r 3 = 3 2 a o 1 = 9 a o
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Bohr Model (1913) Energy of the Orbit E n =- A Z 2 n 2 For H, A = 2.18 x 10 -18 J E 1 A 1 2 1 2 = - A
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VII Atomic Structure and Quantum Theory B - VII Atomic...

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