1. Polarity and Intermolecular Forces
Polarity and Intermolecular Forces. NC Essential Standard , 1.2.5
Polarity and Intermolecular Forces
NC Essential Standard , 1.2.5

2. Electronegativity Measure of attraction for an electron
Most bonds are not completely ionic or covalent, but somewhere in between
Difference in electronegativity determines the nature of bonding
ΔEN > 2.0 ionic (complete transfer)
ΔEN = polar covalent (unequal sharing)
ΔEN = nonpolar covalent (equal sharing)
The ΔEN #s above are strictly a guideline to go by, there is no significant difference between 1.9 and Think of these as a gradual progression from completely nonpolar, ΔEN=0, to completely ionic, ΔEN=3.3 (the greatest possible difference)
Measure of attraction for electrons in molecules. Most bonds are not completely ionic or covalent, but somewhere in between. Differences in electronegativity determines the nature of bonding ΔEN > 2.0 is ionic that is a complete transfer of electrons, ΔEN = is polar covalent that is an unequal sharing of electrons, ΔEN = is nonpolar covalent that is equal sharing of electrons. The ΔEN numbers above are strictly a guideline to go by, there is no significant difference between 1.9 and Think of these as a gradual progression from completely nonpolar, ΔEN=0, to completely ionic, ΔEN=3.3 (the greatest possible difference)

3. Polar Bonds ΔEN =
Unequal Sharing of electrons creates partially positive and negative ends, called a dipole (or simply polar)
Depending on geometry, polar bonds can cause the entire molecule to exhibit polarity (polar molecule)
At the low end, : these molecules may be gases or volatile liquids (example: ammonia, methanol)
At the high end, : these compounds will tend to be solids, although with a much lower melting point than ionic solids (example: sugar, butter)
Unequal Sharing of electrons creates partially positive and negative ends, called a dipole (or simply polar). Depending on geometry, polar bonds can cause the entire molecule to exhibit polarity (polar molecule). At the low end, : these molecules may be gases or volatile liquids (example: ammonia, methanol). At the high end, : these compounds will tend to be solids, although with a much lower melting point than ionic solids (example: sugar, butter)

4. Nonpolar Bonds ΔEN < 0.4
Nonpolar: the electronegativity, or pull on the electrons is close enough that no partially charged regions are created resulting in equal sharing of electrons in bonds
Most nonpolar compounds are gases, but there are some exceptions
Example: methane, oxygen
Nonpolar Bonds: Nonopolar: the electronegativity, or pull on the electrons is close enough that no partially charged regions are created. resulting in equal sharing of electrons in bonds. Most nonpolar compounds are gases, but there are some exceptions. Examples are: methane, oxygen

5. Electronegativity Table
Here is a periodic table with electronegativities. Try predicting the types of bonds based on the differences in electronegativities.

6. Polar Bonds Sometimes Make Polar Molecules
Looking at the ∆EN can tell you if a bond is polar
However, you must visualize the structure to determine if the whole molecule will be polar
Like atoms bonded will always be nonpolar
O2, S8
Different atoms bonded will generally be polar (but need to look at ∆EN)
If the structure has lone pairs of electrons on the central atom, different atoms bonded to the central atom, or anything asymmetrical, it will be POLAR
Symmetrical (shape and atoms) is NONPOLAR
Asymmetrical (shape and/or atoms) is POLAR
Looking at the ∆EN can tell you if a bond is polar. However, you must visualize the structure to determine if the whole molecule will be polar. Like atoms bonded will always be nonpolar O2, S8. Different atoms bonded will generally be polar (but you need to look at ∆EN). If the structure has lone pairs of electrons on the central atom, different atoms bonded to the central atom, or anything asymmetrical, it will be POLAR. Symmetrical (shape and atoms) is NONPOLAR. Asymmetrical (shape and/or atoms) is POLAR.

7. Symmetric Molecules are Nonpolar
Here are some examples of symmetrical nonpolar molecules.

8. Asymmetrical Molecules are Polar
Here are two examples of asymmetrical polar molecules.

9. “Like Dissolves Like” Polarity Effects Solubility
This statement describes the general solubility of substances.
Polar substances dissolve in polar solvents
(such as water)
Nonpolar substances dissolve in nonpolar solvents
(such as gasoline)
Polar and nonpolar substances do not mix
(oil and water)
“Like dissolves like” Polarity Effects Solubility. This statement describes the general solubility of substances.
Polar substances dissolve in polar solvents (such as water). Nonpolar substances dissolve in nonpolar solvents (such as gasoline). Polar and nonpolar substances do not mix (oil and water).

10. Intermolecular Forces: The three types of forces are
Dispersion forces which occur between nonpolar molecules. (Van der Waals)
Dipole-dipole forces which occur between polar molecules.
Hydrogen bonding which occurs between molecules with an H-F, H-O, or H-N bond.
Intermolecular Forces: The three types of forces are 1. Dispersion forces which occur between nonpolar molecules (Van der Waals). 2. Dipole-dipole forces which occur between polar molecules. 3. Hydrogen bonding which occurs between molecules with an H-F, H-O, or H-N bond. Intermolecular forces also determine phase!
Intermolecular forces determine phase!

11. Dipole-Dipole Forces
Dipole-dipole forces occur between molecules with a permanent opposite charges.
Ex:
HCl and HBr
Dipole-dipole forces occur between molecules with a permanent opposite charges. For Example: HCl and HBr molecules.

12. Hydrogen Bonding
Hydrogen bonding is the strongest form of Intermolecular bonds. They are formed when the H of a molecule is attracted to the highly electronegative atom of a neighboring molecule.
Hydrogen bonding is the strongest form of Intermolecular bonds. They are formed when the H of a molecule is attracted to the highly electronegative atom of a neighboring molecule.

13. Note: The larger the molecule the stronger the dispersion forces.
Weakest intermolecular force are the dispersion forces. They occur between nonpolar molecules.
Monatomic molecules: He, Ne, Ar, Kr, etc.
Diatomics with 2 atoms of the same element.
Very symmetric molecules
Note: The larger the molecule the stronger the dispersion forces.
Weakest intermolecular force are the dispersion forces. They occur between nonpolar molecules. 1. Monatomic molecules: He, Ne, Ar, Kr, etc. 2. Diatomics with 2 atoms of the same element. 3. Very symmetric molecules. Note: The larger the molecule the stronger the dispersion forces.

14. Intermolecular bonds Effect M.P, BP, Hv and Hf
Melting pt, Boiling pt, Hf and Hv and vapor pressure depend on how hard it is to pull the particles apart.
Weak intermolecular forces – it’s easy to pull them apart.
Strong intermolecular forces – it’s hard.
Melting point, Boiling point , Hf and Hv and vapor pressure depend on how hard it is to pull the particles apart. For weak intermolecular forces it’s easy to pull them apart. For strong intermolecular forces it’s hard.

15. Which substance has the strongest intermolecular forces? The weakest?
Which substance has the strongest intermolecular forces? Water. The weakest? Diethyl Ether.
Which substance has the strongest intermolecular forces?
The weakest?
Water
Diethyl Ether