Chem 115 Quiz #4

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Name CHM 115 QUIZ #3 Practice Answer the following. Provide as much information as required to answer the question clearly. (5 points) 1. (a) Complete the LEWIS SYMBOLS of the elements listed below by adding the correct number of electrons to each: H C N O Cl (15 points) + 2. For the following molecules and ion CO, N2, NO, N2 , do the following: (a) Draw the Lewis structure (use resonance ONLY if it is needed). Also, calculate and SHOW the formal charge on each atom in each structure, (find the average formal charge if you used resonance structures) CO N2 :C≡O: :N≡N: -1 +1 0 0 + NO N2 :N=O + + ⋅N≡N: ÅÆ :N≡N⋅ 0 0 +1 0 0 +1 1 AveFC (N) = + /2 Which of the structures do not obey the octet rule? Explain why not? + The NO and the N2 do not obey the octet rule. In both of these cases, the species (molecule and ion) are odd electron species and MUST have an atom that does not have a full octet. In the case of NO, the oxygen is the atom that gets the full octet (it is more electronegative than is N) while N is left with seven electrons. However, both the O and the N both have formal charges of zero. In the case of N2+, resonance structures must be drawn to show that the ionic charge is uniformly shared by the two N in the ion. Each of the ions carries an average formal charge of 1 + /2. (continued) (8 points) 3. In the space below do the following: draw the best Lewis structures of the species PCl3 and PCl5. Comment on the number of electrons around the P atom in each structure. The P atom in PCl3 obeys the octet rule while the P atom in the PCl5 has ten (10) electrons around it (an expanded octet). The expansion of octets may occur for atoms beyond period 2 in the periodic table. (22 points) 4. For the following two species complete the tasks specified below in a – d. i. CH3COOH ii. C2H4 a. Draw the best Lewis structures. b. Specify the hybridization 3 C in CH C in CH3 sp 2 2 of both sp 2 the C atoms and the O atom C in CO sp specified in (i) 3 and the C atoms in (ii)? O between CO and H sp c. Show the energy level C in CH3 C in CH2 diagram for both the C atoms and the O atom in (i) and the ↑ ↑ ↑ ↑ For both C C atoms in (ii), fill the σ σ σ σ diagrams with the correct ↑ ↑ ↑ ↑ number of valence electrons, C in CO π and identify the types of σ σ σ ↑ electrons present (i.e. σ, π, ↑ ↑ ↑ lone pair) π σ σ σ O between CO and H ↑↓ ↑↓ ↑ ↑ lp lp σ σ d. What are the bond angles C in CH3 ~109.5° C in CH2 120° around both the C atoms and the O atom in (i) and the C C in CO ~120° atoms in (ii)? O between CO and H ~109.5° .

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