CHEMISTRY 1E03-01 TUTORIAL #6

Dr. J. D. Laposa October 26 - 30, 1998

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NOTE: All Chem 1E03-01 students will have a formal tutorial during the week of October 26. Solutions will be posted.

1. For each of the following twelve species, draw an adequate Lewis structure, including formal charges, give the AXnEm class, predict the shape, and state if the octet rule is being violated.

a) Cl2O

There are 20 valence electrons. The Lewis structure is:

The molecule is AX2E2, and is bent.

b) H2CO

There are 12 valence electrons. The Lewis structure is:

The molecule is AX3, and is triangular planar.

c) SF4

There are 34 valence electrons. The Lewis structure is:

Note that the nbp on S is an equatorial nbp.

The molecule is AX4E, and has a seesaw shape (or distorted tetrahedron).
Note that a 2-dimensional Lewis structure does not show the shape. (The shape is inferred from the VSEPR treatment.)

The octet rule is violated here.

d) CCl2Br2

There are 32 valence electrons.

The molecule is AX4, and is tetrahedral.

e) ICl3

There are 28 valence electrons. The Lewis structure is:

The molecule is AX3E2, and is T-shaped (the 2 nbps are equatorial).

The octet rule is violated here.

f) IF5

There are 42 valence electrons. The Lewis structure is:

The molecule is AX5E, and is square-based pyramidal.

The octet rule is violated here.

g) PF5

There are 40 valence electrons. The Lewis structure is:

The molecule is AX5, and is triangular bipyramidal.

The octet rule is violated here.

h) NO2-

There are 18 valence electrons. The Lewis structure is:

The ion is AX2E, and is bent.

We will soon see that there are two resonance structures for NO2-; this is one of them; both N-O bonds are equivalent.

i) SO3

There are 24 valence electrons. The Lewis structure is:

The molecule is AX3, and is triangular planar.

The octet rule is violated here.

j) SO32-

There are 26 valence electrons. The Lewis structure is:

The molecule is AX3E, and is triangular pyramidal.

The octet rule is violated here.

There are three resonance structures for SO32-;this is one of them;all three S-O bonds are equivalent.

k) OCS

There are 16 valence electrons. The Lewis structure is:

The molecule is AX2, and is linear.

l) PO43-

There are 32 valence electrons. The Lewis structure is:

The molecule is AX4, and is tetrahedral.

The octet rule is violated here.

There are four resonance structures for PO43-;this is one of them;all four P-O bonds are equivalent.

2. Match the molecules SiH4, PI3, BBr3, GeCl2, and SF6 with the bond angles 90o, 109.5o, 120o, slightly less than 109.5o, and slightly less than 120o
.

SiH4, an 8 valence electron system, is AX4; it has 109.5o bond angles.

PI3, a 26 valence electron system, is AX3E; its bond angles are slightly less than 109.5o.

BBr3, a 24 valence electron system, is AX3; it has 120o bond angles.

GeCl2, an 18 valence electron system, is AX2E; its bond angle is slightly less than 120o.

SF6, a 48 valence electron system, is AX6;it has 90o bond angles.

(Hint: for all of these species, count the valence electrons, deduce the AXnEm class, and determine the geometry. With sufficient practice, you can often do these steps without drawing a Lewis structure.)