1. Intermolecular Forces

2. Ionic vs. Covalent
The higher the boiling point and melting point of a substance the stronger the forces between the particles
Forces of attraction between ions is stronger than between molecules
Ionic compounds have much higher boiling and melting points than covalent compounds

3. Ionic Compounds
The smaller the ion the stronger the force of attraction
Larger ions are farther apart so attractive forces are weaker

4. Intermolecular Forces
Forces that act between molecules (basic units of covalent compounds)
Van Der Waals forces
Dipole-dipole forces
Hydrogen bonding
London Dispersion forces

5. Dipole-Dipole Forces
Positive end of one molecule attracts the negative end of another molecule
Charged ends of molecules result from uneven sharing of electrons (polar bonds)
The bigger the difference of electronegativity of the atoms the more polar the bond
The more polar the molecule the stronger the dipole-dipole forces
thus the higher the melting and boiling point

6. Hydrogen Bonds Special dipole-dipole force
Stronger than regular dipole-dipole
Involve H atoms and very electronegative atoms
The H becomes partially positive and is attracted to unshared pairs of electrons on other molecules
So strong because of high electronegativity difference and hydrogen’s small size

7. Properties of Water Some the result of H bonding
Water can form multiple H bonds
Solid less dense than liquid because of shape of molecule

9. London Dispersion Forces
Special dipole-dipole force
Act on nonpolar substances
Larger molecules stronger forces
Proportional to the number of electrons
Temporary dipoles are created
Briefly ends of a molecule can become (+) or (-) called induced dipoles
Attraction between temporary dipoles holds the molecules together

10. Relative Strength Strongest to weakest Ionic attraction
Covalent Bonding
H bonding
Dipole-Dipole
London Dispersion

11. Properties Determined by the IMF acting Size and shape play a role
Stronger forces gives higher melting and boiling points
Size and shape play a role
Larger particles are farther apart, decreasing the strength of the forces
The shape can keep things closer together or farther apart thus affecting the strength of the IMF

12. Surface Tension
Force that acts on the surface of a liquid and that tends to minimize the area of a surface
To increase the surface area requires energy
Most liquids make spheres because spheres have the lowest surface area per volume.

13. Cohesion/Adhesion
Cohesion- liquid particles have an attraction for each other
Adhesion- liquid particles have an attraction for particles of solid surfaces
Combo of cohesion and adhesion create capillary action