1. Chapter 6
The Shape of Molecules

2. Are all Covalent Bonds Created Equal?
Electronegativity (E.N.) causes different types of covalent bonds!
High EN= greater ability to take electrons
Nonmetals …
Metals …
Metals can lose electrons to nonmetals to form ionic bonds…but what happens with two nonmetals?

3. Electronegativity (E.N.)

4. Covalent Bond Classification
Electronegativity and Covalent Bond Types
Two atoms with identical E.N. result in pure covalent bonding…
Which means..
Different E.N. causes polar covalent bonding…
Which means…

5. Covalent Bond Classification
Electronegativity difference (EN)
Relationship between EN and bond polarity:

6. Classifying Bonds based on EN
Greater EN means more polarity
EN difference below 0.5 =
EN Difference “ish” =
EN difference greater than 1.9 =

7. Classifying Bonds based on EN
Classify the bond type of the following compounds based on EN difference
H2O (between one H and the O)
NH3 (between one H and the N)
Cl2
RbCl
Which has the greatest ionic character?
Which is most polar?
Which has the greatest covalent character?

8. 6.2 Valence Shell Electron Pair Repulsion (VSEPR) Theory
Valence shell electron pair repulsion theory
Bond type does not fully determine shape!
VSEPR Model is used to predict three-dimensional shapes of molecules.
Based on how negative charges on electrons repel one another…
the electrons move as far apart as possible!

9. Steps in using VSEPR theory:
Draw the electron dot diagram
Find the steric number for the atom
Predict the molecular shape…
SN of 4 = tetrahedral
SN of 3= trigonal planar
SN of 2 = linear
4. Account for lone (non-bonding) pairs
SN 4, one lone pair = PYRAMIDAL
SN 4, two lone pairs= BENT
SN 3, one lone pair= BENT

10. 6.2 VSEPR Theory

11. 6.2 VSEPR Theory

12. 6.2 VSEPR Theory Methane (CH4) How many bonding electron pairs?
Steric number = ___________, ____________
What shape?
Why?

13. 6.2 VSEPR Theory
Predict the shape of NH3
1. Draw the electron dot diagram.
2. Find the steric number for the atom.
3. Predict the maximum angle.
But…

14. Molecular Polarity= distribution of electrons
6.3 Polarity of Molecules
Molecular Polarity= distribution of electrons
Related to bond polarity but not the same
Related to the molecule shape:
Even electron distribution=
Uneven electron distribution =
Polar molecules:
Nonpolar molecules:

15. Consider bonding in H2 and HF
6.3 Polarity of Molecules
Consider bonding in H2 and HF
H2 is _______________________
HF is ______________________
Describe the e arrangement on each:
Describe the partial charges on each:

16. 6.3 Polarity of Molecules Molecular polarity H2 is a nonpolar molecule
Electrons are equally distributed, even charge
HF and HCl are polar molecules
Why?
How?

17. Showing molecular polarity
6.3 Polarity of Molecules
Showing molecular polarity
Dipole moment vectors:
Long arrow means:

18. Dipole moment and molecular polarity
6.3 Polarity of Molecules
Dipole moment and molecular polarity
Dipoles in an asymmetrical molecule don’t cancel
What’s this mean?
Dipoles in linear or symmetrical molecules cancel out because they go in opposite directions

19. 6.3 Polarity of Molecules
Determine if each of these is polar or nonpolar…
Phosphorus trichloride
Ammonia (nitrogen trihydride)
Ethene C2H4 (don’t forget the C=C)

20. 6.2 Valence Shell Electron Pair Repulsion (VSEPR) Theory (Continued)
PBr3
Draw the Lewis Structure with electron groups
Find the SN
Determine the electron arrangement shape
Determine the true molecular shape