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Intermolecular Forces

Intermolecular Forces. Pat, Louis, Graham. Brief Info. It is the attraction between molecules Require much less energy to overcome attraction than to break the bond

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Intermolecular Forces

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  1. Intermolecular Forces Pat, Louis, Graham

  2. Brief Info • It is the attraction between molecules • Require much less energy to overcome attraction than to break the bond • Ex: takes only 16 kJ/mol to overcome attraction between HCl molecules (change from liquid to gas), rather then 431 kJ/mol to dissociate HCl into H and Cl atoms • The greater the attraction force, the more energy required to break them

  3. Ion-Dipole Forces • Exist between an ion and partial charge end of a polar molecule • Positive ions are attracted to negative end of a dipole • Negative ions are attracted to the positive end of a polar dipole • Attraction increases as charges from ion increases or charge of dipole increases

  4. Ion-Dipole Force

  5. Dipole-Dipole Forces • Attractive force between the positive and negative ends of molecules • Only form when molecules are close together • Generally much weaker than ion-dipole forces • The stronger the polarity, the stronger the forces are • Molecules with similar polarity will have higher dipole-dipole forces than others

  6. Dipole-Dipole Forces

  7. London Dispersion Forces • Attraction between molecules and atoms that normally seem nonpolar • It is an instantaneous dipole moment • When the atom is frozen within that moment in time where more electrons are on one side more than the other

  8. London Dispersion Forces • At this exact moment, there is a dipole moment, creating an attraction between the molecules • Polarizability- ease with which charge distribution can be distorted by external electric field • Ex: nearby atoms or molecules can cause the electrons to repel to one side, causing this dipole moment

  9. London Dispersion Forces • The more polarizable a molecule is, the stronger the London Dispersion Force is • Generally, larger molecules have greater polarizabilty due to more electrons, causing them to be further from the nuclei • Molecules with similar weights and shape have equal attraction • Molecules that differ in weight or shape will have uneven forces, the larger molecule has the stronger attraction

  10. Hydrogen Bonds • The attraction between molecules with hydrogen • Ex: the attraction between H2O molecules

  11. Hydrogen Bonding • Hydrogen atoms have no extra electron, leaving it’s proton exposed • This causes hydrogen to form an attraction to a negative charged electronegative atom of another molecule • This attraction is weaker than chemical bonds but are stronger than dipole-dipole bonds and dispersion forces

  12. Different Intermolecular Forces • Dispersion forces are located in all substance • Dipole-dipole forces are only located in polar molecules • Hydrogen bonds are only available when H is bonded to either N, O, or F • Hydrogen bonds tend to be the strongest of these attractions • None of these are stronger than covalent or ionic bonds

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