Intermolecular Bonds:

Types of Bonds:

1. Intramolecular bonds = within a molecule (*think intramural)
    - Ionic + Covalent

2. Intermolecular bonds = between molecules (*think international)
    - The stronger the intermolecular bonds the higher the BP or MP
    - 2 Types: Vander Waals bonds & Hydrogen bonds

Vander Waals Bonds:

• Based on electron distribution
• 2 Categories: 

1. Dipole - Dipole bonds 

• if a molec. is Polar, the + end of one molec will be attracted to the - end of another molec. 

     2.  London Dispersion Forces (LDF)

• present in all molecs
• creates the weakest bonds 
• if a substance is non-polar Dipole - Dipole forces don't exist 
• electrons are free to move around & will randomly be grouped on one side of the molec. 
• Creates a temporary dipole and can cause a weak bond to form
• the more e- in the molec. the stronger the LDF will be

EX//

- NH3 (10e) VS. C2H8 (18e)
  polar                  non-polar

- NH3 has the stronger bond because of it's Dipole-Dipole bond.  C2H8 is non-polar thus it's bond is LDF making it's bond weaker than NH3.

Hydrogen Bonding:

• if hydrogen bonded to certain elements (F, O, & N) the bond is highly polar 
• this forms a very strong intermolecular bond.  

EX//

- H2O (10e) VS. CH4 (10e)
  Polar                 Polar

- They are both Polar and both have the same amount of e- but H2O wins for the highest boiling point due to its Hydrogen bond.

A very helpful Video... :)

 

Polar Molecules

What is polarity?

In chemistry polarity refers to a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds. Molecular polarity is dependent on the difference in electronegativity between atoms in a compound and the asymmetry of the compound's structure.

*Things to remember

• Polar molecules have an average charge seperation
• Unsymmetrical molecules are usually polar
• Molecular dipoles are the result of un = sharing of electrons in a molecule

Predicting Polarity

• If a molecule is symmetrical, the pull of e- is usually balanced 
• Molecules can be un-symmetrical in 2 ways

-- Diff atoms

-- Diff # of atoms

A molecule can possess polar bonds and still be nonpolar. If the polar bonds are evenly (or symmetrically) distributed, the bond dipoles cancel and do not create a molecular dipole. 

Here's a video that will explain things a bit more clearly....

Bonds

There are 3 main types of bonds in chemistry

1. Ionic (metal to non-metal)
Electrons are transferred from metal to non-metal

2. Covalent (non-metal to non-metal)
Electrons are shared between non-metals

3. Last but not least, Metallic (metal)
Holds pure metals together by electrostatic attraction

Electronegativity (en) is a measure of an atom's attraction for electrons in a bond

Atoms with greater electronegativity attract electrons

Polar Covalent bonds form from an unequal sharing of electrons, a polar covalent bond is a bond between two non-metals with different electronegativities. Unsymmetrical molecules are usually polar.
Non-Polar covalent bonds form from equal sharing of electrons, and are symmetrical molecules.
The type of bond formed can be predicted by looking at the difference in electronegativity (en) of the elements



Here are some examples!


Predict the type of bond formed.


1. H- O

2.20 - 3.44 = 1.24
This bond between Hydrogen and Oxygen is a Polar Covalent bond!


2. K-F


3.99 - 0.82 = 3.17
This bond between potassium and fluorine is an Ionic bond!

Now that we went through some examples together, let's see if you can do some on your own!

QUIZ TIME!!!! (: