5. dipole-dipole interactions occur between polar molecules London Dispersion Forces occur between all molecules (polar and non-polar) There are two types of intermolecular forces
6. The partial charges in polar molecules cause attractions and repulsions between separate polar molecules A hydrogen bond is a specific type of dipole-dipole interaction that is extra strong DIPOLE-DIPOLE INTERACTIONS
7. HYDROGEN BOND A molecule can H-bond if it contains hydrogen bound to an atom with high electronegativity (N, O, or F)
8. IN THIS CASE- The especially strong partial charge ( δ + ) on hydrogen makes it “stick” to anything negative. Hydrogen bonding
9. No one in the corner grabs electrons like us! – N, O, & F N O F
11. London Dispersion Forces A covalent molecule consists of atoms bound by overlapping electron clouds. Sometimes these electron clouds have temporary “thin or thick spots” causing temporary partial charges.
12. These temporary partial charges can cause temporary partial charges on other molecules or atoms. London Dispersion Forces
13. Temporary partial charges experience attractions and repulsions just like permanent partial charges and ion charges. London Dispersion Forces
14. The larger the molecule the larger the London Dispersion Forces
15. What is the difference between the partial charges on a polar molecule (which cause dipole-dipole interactions) and the partial charges that cause London Dispersion attractions?
17. The stronger the intermolecular forces the more likely the compound will be a solid at room temperature.
18. Compounds with weak intermolecular forces have low boiling and melting points. Strong intermolecular forces require a lot of energy to overcome, so compounds with strong intermolecular forces have high melting and boiling points. Liquids with strong intermolecular forces will hold on to their molecules preventing them from escaping as a vapor.
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20. Intermolecular forces Weakest lower melting point Dispersion forces Dipole-dipole interactions Hydrogen 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
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23. TYPES OF SOLIDS ionic solids – made of ions held together by ionic bonds molecular solids - made of molecules held together by intermolecular forces metallic solids - atoms held together by metallic bonds(sea of electrons model) network solids - atoms held together by covalent bonds
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26. Would you expect the following solids to have a relatively high or low melting point? Metal Ionic solid Non-polar molecular solid Polar molecular solid Atomic solid of a noble gas Network solid
Editor's Notes
Diamond is a network-solid form of carbon. Diamond has a three-dimensional structure, with each carbon at the center of a tetrahedron.