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FALL2006_Exam_3_key[1]

# FALL2006_Exam_3_key[1] - CHEM 109 EXAM 3 FALL 2006 SHOW ALL...

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CHEM 109 EXAM 3 FALL 2006 – SHOW ALL WORK – NO WORK – NO CREDIT 1. (10 pts.) The “clickers” used in class could transmit at a wavelength of 2.75 x 10 3 nm. (a) What is the frequency of this radiation? c = νλ ; 3.00 x 10 8 m/s = (2.75 x 10 –6 )( ν ); = 1.09 x 10 14 _______________ Hz (b) Calculate the energy, in Joules, of one photon of this radiation. E = hc/ λ ; or E = h ; (6.626 x 10 –34 )(1.09 x10 14 ) = 7.23 x 10 –20 _______________ J (c) Consider the following frequencies emitted by two different clickers in class and answer the following questions by circling your choice: Clicker 1: 1.10 x 10 14 Hz Clicker 2: 8.00 x 10 13 Hz (i) Which has the largest wavelength? Clicker 1 Clicker 2 Can’t tell (ii) Which has the largest energy? Clicker 1 Clicker 2 Can’t tell (iii) Which emits the most photons? Clicker 1 Clicker 2 Can’t tell 2. (10 pts.) (a) Excited hydrogen atoms in a star emit light with a wavelength of 656.5 nm. If the electron starts out in the n =3 level, to what level does this electron fall in this emission process? Hint: Think about the direction of energy exchange! E = hc/ ; E = (6.626 x 10 –34 )(3.00 x 10 8 m/s)/(656.5 x 10 –9 )= 3.0278 x 10 –19 E = –2.18 x 10 –18 [Z 2 /n 2 f – Z 2 /n 2 i ]; –3.0278 x 10 –19 = –2.18 x 10 –18 [1 2 /n 2 f – 1 2 /3 2 ] (Energy is EXOTHERMIC!) Rearrange and combine like terms: 1/n 2 = 0.2500; n 2 = 4; n = 2 n final = 2 (b) An excited-state atom absorbs photons when electrons leap between the levels marked as a, b, and c in the atomic energy level diagram below. The wavelengths of the emitted photons are 657 nm, 122 nm, and 103 nm (not necessarily in the proper sequence). Match each absorption line, marked as (i), (ii) and (iii) , with the appropriate wavelength. E = hc/ ; 1 a b c (i) (ii) (iii) (i) 103 nm (ii) 122 nm (iii) 657 nm

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CHEM 109 EXAM 3 FALL 2006 – SHOW ALL WORK – NO WORK – NO CREDIT 3. (10 pts.) Several scientists proposed theories that led to today’s quantum mechanical view of electrons. In the chart below, match each scientist with their contribution(s) by placing a check in the boxes that correspond to the statements found below. Check any and all descriptions and diagrams that apply for each scientist. Some scientists may have more than one contribution.
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FALL2006_Exam_3_key[1] - CHEM 109 EXAM 3 FALL 2006 SHOW ALL...

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