If you cannot draw lewis dot you need to review chapter 6 section 3. (pp. 208-213)
Intermolecular Forces are forces between two or more molecules. 11.2 IMF
Intermolecular attractions are weaker than ionic & covalent bonds. These attractions determine whether a molecular compound is a gas, a liquid, or a solid.
Ionic vs Covalent
Ionic compounds have a larger force of attraction than covalent compounds.
The larger the charge the stronger the force of attraction.
Stronger force of attraction = harder to separate.
Higher boiling point
Higher melting point
3 Intermolecular Forces
London-Dispersion Forces (LDF)
Between polar molecules.
More polar = stronger forces.
Stronger force = higher boiling point.
A form of dipole-dipole.
A molecule can H-bond if it contains hydrogen bond to an atom with high electronegativity ( N, O, or F )
No one in the corner grabs electrons like us! – N, O, & F N O F
London Dispersion Forces (LDF)
Weakest of all the IMF.
Occur between all molecules.
Larger molecules have a larger LDF.
Partial positive Partial negative
These temporary partial charges can cause temporary partial charges on other molecules or atoms. London Dispersion Forces
Stronger intermolecular force = a solid at room temperature. dipole-dipole or hydrogen bond usually means solid.
Weak intermolecular forces = low boiling and low melting points. Strong intermolecular forces = high melting and high boiling points. Liquids with strong intermolecular forces will hold on to their molecules preventing them from escaping as a vapor.
Solid - Strong intermolecular forces hold molecules in a rigid & regular pattern (crystal).
Liquid - Some intermolecular forces are overcome and molecules can slip past each other.
Gas - Weak intermolecular forces can’t hold molecules together, so each molecule is free and independent.
States of Matter
Intermolecular forces Weakest lower melting point LDF Dipole-dipole H-bonds STRONGEST higher melting point Ionic compounds have even higher melting points because the ionic bond must be overcome to free the ions. Ionic bonds are much stronger than any intermolecular force. Intermolecular Forces