CH 152 Lewis Diagram Practice Jan 16, 2003

(A Homework Exercise)

1. Give several examples for which the following statement proves to be incorrect. "All atoms in a Lewis structure have an octet of electrons in their valence shells.

2. Which of the following have Lewis structures that do not obey the octet rule: NH3, BF3, SF6, SO3, NH4+, SO42-, NO2? Explain.

3. By means of Lewis structures, represent bonding between the following pairs of elements: (a) Cs and Br; (b) H and Sb; (c) B and Cl; (d) Cs and Cl; (e) Li and O; (f) Cl and I. Your structures should show whether the bonding is essentially ionic or covalent.

4. Suggest reasons why the following do not exist as stable molecules: (a) H3 (b) HHe; (c) He2; (d) H3O.

5. Only one of the following Lewis structures is correct. Select that one and indicate the errors in the others. .. ..
(a) cyanate ion [ :O ¾ C == N : ]
ŸŸ

(b) carbide ion [ : C ºº C : ]2-

.. ..
(c) hypochlorite ion [: Cl ¾ O : ]-
ŸŸ ŸŸ
.. ..
(d) nitrogen(II) oxide : N ¾ O :

6. Indicate what is wrong with each of the following Lewis structures. Replace each with a more acceptable structure.
..
(a) Mg : O :
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.. .. ..
(b) [ :Cl ]+[ :O: ]2-[ Cl: ]+
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.. . ..
(c) [ :O ¾ N == O: ]+

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(d) [ :S ¾ C == N: ]-

7. Write acceptable Lewis structures for the following molecules:
(a) H2NOH; (b) HOClO2; (c) HONO; (d) O2SCl2.

8. The following polyatomic anions involve covalent bonds between O atoms and the central nonmetal atom. Propose an acceptable Lewis structure for each. (a) SO32-; (b) NO2-; (c)CO32-; (d) HO2-.

9. Write a plausible Lewis structure for crotonaldehyde, CH3CHCHCHO, a substance used in tear gas and insecticides.