Intermolecular Bonds

Types of Bonds
- Intramolecular bonds
   - exist within a molecule
   - ionic, covalent
- Intermolecular bonds exist between molecules
   - The stronger the intermolecular bonds the higher the boiling point or melting point
   - Two types of Intermolecular : Van der Waals Bonds and Hydrogen bonds

Van der Waals Bonds
- Based on electron distribution
- Two categories
1) Dipole - Dipole bonds
    - If a molecule is polar the positive end of one molecule will be attracted to the negative end of another      molecule
2) London Dispersion Forces (LDF)
    - LDF is present in all molecules
    - creates weakest bonds
    - if a substance is non-polar dipole-dipole forces don't exist
    - Electrons are free to move around and will randomly be grouped on one side of the molecule
    - This creates a temporary dipole and can cause a weak bond to form
    - The more electrons in the molecule the stronger the LDF can be

Hydrogen Bonding
- If Hydrogen is bonded to certain elements (F, O, or N) the bond is highly polar
- This forms a very strong intermolecular bond

Effects of Bonds
- Melting and boiling points are a measure of intermolecular bond strength

- JanCarlo Paysan

Polar Molecules

Polar Molecules
- Polar molecules have an overall charge separation
- Unsymmetrical molecules are usually polar
- Molecular dipoles are the result of unequal sharing of electrons in a molecule

Predicting Polarity
- If a molecule is symmetrical the pull of electrons is usually balanced
- Molecules can be unsymmetrical in two ways
   - different atoms
   - different number of atoms

- JanCarlo Paysan

Bonding

Bonds & Electronegativity

Types of Bonds
- There are 3 main types of bonds:

1) Ionic (metal - non metal)
     - electrons are transferred from metal to non metal
2) Covalent (non metal - non metal)
     - electrons are shared between non metals
3) Metallic (metal)
     - holds pure metals together by electrostatic attraction

Electro Negativity
- Electro negativity (en) is a measure of an atom's attraction for electrons in a bond
- Atoms with a greater en attract electrons more
- Polar Covalent bonds form from an unequal sharing of electrons
- Non-Polar Covalent bonds form from equal sharing

Bonds
- The type of bond formed can be predicted by looking at the difference in electronegativity of the elements
    - en > 1.7 = ionic bond
    - en < 1.7 = polar covalent bond
    - en = 0 = non polar covalent bond

- Jan Carlo Paysan