Chapter 4: Problem 34
Write Lewis structures and predict whether each of the following is polar or nonpolar. a. HOCN (exists as HO-CN) b. cos c. \(\mathrm{XeF}_{2}\) d. \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) e. \(\operatorname{SeF}_{6}\) f. \(\mathrm{H}_{2} \mathrm{CO}(\mathrm{C}\) is the central atom.)
Short Answer
Expert verified
a. HOCN is nonpolar with a linear molecular geometry.
b. COS is polar with a linear molecular geometry.
c. XeF2 is nonpolar with a linear molecular geometry.
d. CF2Cl2 is nonpolar with a tetrahedral molecular geometry.
e. SeF6 is nonpolar with an octahedral molecular geometry.
f. H2CO is polar with a trigonal planar molecular geometry.
Step by step solution
01
Draw the Lewis structure
We start by counting the valence electrons: H has 1, O has 6, C has 4, and N has 5. In total, there are 16 valence electrons. Following the octet rule, the Lewis structure for HOCN is:
```
H - O - C ≡ N
```
02
Electron pair geometry and molecular geometry
The central atom, carbon, has a double bond with oxygen and a triple bond with nitrogen. Thus the electron pair geometry is linear, and the molecular geometry is also linear.
03
Check for a net dipole moment
The bond dipoles cancel each other out, resulting in a net dipole moment of zero. Therefore, the molecule is nonpolar.
#b. COS
04
Draw the Lewis structure
We start by counting the valence electrons: C has 4, O has 6, and S has 6. In total, there are 16 valence electrons. Following the octet rule, the Lewis structure for COS is:
```
O = C = S
```
05
Electron pair geometry and molecular geometry
The central atom, carbon, has a double bond with oxygen and a double bond with sulfur. The electron pair and molecular geometry are both linear.
06
Check for a net dipole moment
The bond dipoles do not cancel each other out, resulting in a net dipole moment. Therefore, the molecule is polar.
#c. XeF2
07
Draw the Lewis structure
We start by counting the valence electrons: Xe has 8, and each F has 7, resulting in a total of 22 valence electrons. The Lewis structure for XeF2 is:
```
F
|
Xe - F
```
08
Electron pair geometry and molecular geometry
The central atom, Xenon, is bonded to two fluorine atoms, and there are three lone electron pairs on Xenon. The electron pair geometry is octahedral, and the molecular geometry is linear.
09
Check for a net dipole moment
The bond dipoles cancel each other out, resulting in a net dipole moment of zero. Therefore, the molecule is nonpolar.
#d. CF2Cl2
10
Draw the Lewis structure
We start by counting the valence electrons: C has 4, each F has 7, and each Cl has 7, resulting in a total of 32 valence electrons. The Lewis structure for CF2Cl2 is:
```
F - C - F
| |
Cl Cl
```
11
Electron pair geometry and molecular geometry
The central atom, carbon, forms single bonds with 2 fluorine and 2 chlorine atoms. Both the electron pair and molecular geometries are tetrahedral.
12
Check for a net dipole moment
Although there are polar bonds between the central carbon atom and the fluorine and chlorine atoms, their positions and bond dipoles cancel each other out, resulting in a zero net dipole moment. Therefore, the molecule is nonpolar.
#e. SeF6
13
Draw the Lewis structure
We start by counting the valence electrons: Se has 6, and each F has 7, resulting in a total of 48 valence electrons. The Lewis structure for SeF6 is:
```
F
|
F - Se - F
| |
F F
|
F
```
14
Electron pair geometry and molecular geometry
The central atom, selenium, has six bonded fluorine atoms, and its electron pair geometry is octahedral. The molecular geometry is also octahedral.
15
Check for a net dipole moment
The bond dipoles cancel each other out, resulting in a net dipole moment of zero. Therefore, the molecule is nonpolar.
#f. H2CO (C is the central atom)
16
Draw the Lewis structure
We start by counting the valence electrons: C has 4, O has 6, and each H has 1, resulting in a total of 12 valence electrons. The Lewis structure for H2CO is:
```
H
|
H - C = O
```
17
Electron pair geometry and molecular geometry
The central atom, carbon, has a single bond with hydrogen atoms and a double bond with an oxygen atom. The electron pair geometry is trigonal planar, and the molecular geometry is also trigonal planar.
18
Check for a net dipole moment
The bond dipoles do not cancel each other out, resulting in a net dipole moment. Therefore, the molecule is polar.
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