1. Bond Lengths and Energies
Lesson Seven

2. Bond Angles

3. Dipoles
Remember that dipoles in molecules are created from the electronegativity of the atoms within the molecule
The greater the electronegativity, the greater the dipole within a molecule and the stronger the bond

4. Bond Lengths and Energies
The distance between two bonded atoms at their minimum potential energy is the average distance between two bonded atoms, is the bond length
In forming a covalent bond, atoms need to release energy as they change from isolated individual atoms to parts of a molecule
Bond energy is the energy required to break a chemical bong and form neutral isolate atoms
This is usually measured in kJ/mol

5. Bond Lengths and Energies
The greater the bond length, the smaller the bond energy required to break apart the attraction between the two atoms
As the electronegativity difference increases, the more tighter the atoms are held to one another
Within bond lengths of the same atom, the larger the atom, the greater the bond length

6. Bond Lengths and Energies
Bond Length (pm)
Bond Energy (kJ/mol)
H-H 74
436
C-C
154
346
F-F
141
159
C-N
147
305
Cl-Cl
199
243
C-O
143
358
Br-Br
228
193
C-H
109
418
I-I
267
151
C-Cl
177
327
H-F 92
569
C-Br
194
285
H-Cl
127
432
N-N
145
163
H-Br
366
N-H
101
386
H-I
161
299
O-H 96
459

7. Class Work
Now that we’ve discussed ideal angles in the molecular geometries and discussed ideal bond lengths and energies within diatomic molecules, let’s observe how these guidelines compare to more complicated atoms that involve more that two atoms
Work through this website and record information on ten molecules of different shapes
Record their Lewis structure, VSEPR shape, bond angles, bond lengths, and energy

8. Click on these options to search molecules by atom, or by shape to look for specific molecules
By clicking on an atom, you will be shown all of the molecules in the database that contain this molecule. Click on more than one atom to refine your search to molecules containing those atoms

9. Once you’ve selected a molecule, observe the experimental bond lengths and angles for that molecule. How do they compare to literature values? Are there differences? If there are, account for these differences using what you know about dipoles and the VSEPR theory.
Play around in the window to rotate the molecule and zoom in/out, and many other options