Chapter 3: Shapes and Polarity of Chemical Species

Question 1

how do you represent atoms projecting into or out of the paper in prospective diagrams (2)

Answer 1

• bonds orientated out of the page or indicated by a solid wedge
• bonds that extend behind the plane of the paper are indicated by a dashed wedge

Question 2

what does the VESPR theory stand for and how does it work (2)

Answer 2

• Valence-Shell-Electron-Pair-Repulsion theory
• as a consequence of repulsion between valence electron pairs, all pairs are oriented as far away as possible from each other in 3-D space: minimizes net electrostatic repulsion making the overall energy of the molecule minimized

Question 3

E = 0
X = 2

Answer 3

linear

180

Question 4

E = 0
X = 3

Answer 4

trigonal planar

120

Question 5

E = 1
X = 2

Answer 5

molecular shape: bent
parent shape: trigonal planar
120

Question 6

E = 0
X = 4

Answer 6

tetrahedral

109.5

Question 7

E = 1
X = 3

Answer 7

molecular shape: trigonal pyramidal
parent shape: tetrahedral
109.5

Question 8

E = 2
X = 2

Answer 8

molecular shape: bent
parent shape: tetrahedral
109.5

Question 9

E = 0
X = 5

Answer 9

trigonal bipyramidal
eq-ax 90
eq-eq 120
ax-ax 180

Question 10

E = 1
X = 4

Answer 10

molecular shape: seesaw 
parent shape: trigonal bipyramidal
eq-ax 90
eq-eq 120
ax-ax 180

Question 11

E = 2
X = 3

Answer 11

molecular shape: t-shaped
parent shape: trigonal bipyramidal
eq-ax 90
ax-ax 180

Question 12

E = 3
X = 2

Answer 12

molecular shape: linear
parent shape: trigonal bipyramidal
ax-ax 180

Question 13

E = 0
X = 6

Answer 13

octahedral
eq-eq, eq-ax 90
ax-ax 180

Question 14

E = 1
X = 5

Answer 14

molecular shape: square-based pyramidal
parent shape: octahedral
eq-eq, eq-ax 90
ax-ax 180

Question 15

E = 2
X = 4

Answer 15

molecular shape: square planar
parent shape: octahedral
eq-eq 90

Question 16

E = 0
X = 7

Answer 16

pentagonal pyramidal
eq-eq 72
ax-eq 90
ax-ax 180

Question 17

what is the procedure for determining polarity

Answer 17

1. determine the molecular shape and draw a perspective diagram
2. draw bond dipoles for all the bonds, indicating both direction and relative magnitude of each bond dipole
3. sum the dipole vectors, if the vector is zero the molecule is non-polar; if the vector is non-zero, the molecule is polar and has a net dipole moment which can be represented by a vector arrow