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Lecture 5.1 – Intermolecular Forces and the Dissolving Process

Lecture 5.1 – Intermolecular Forces and the Dissolving Process. Today’s Learning Targets. LT 4.1 – I can discuss how ionic solids dissolve due to the random molecular motion of the water molecules.

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Lecture 5.1 – Intermolecular Forces and the Dissolving Process

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  1. Lecture 5.1 – Intermolecular Forces and the Dissolving Process

  2. Today’s Learning Targets • LT 4.1 – I can discuss how ionic solids dissolve due to the random molecular motion of the water molecules. • LT 4.2 – I can identify a compound as containing hydrogen bonding, dipole – dipole forces, and Van der Waals forces. • LT 4.3 – I can compare and contrast various intermolecular forces and relate them to the dissolving process of a solid.

  3. What do solids, liquids, and gases look like?

  4. I. Solids • Atoms in a solid hold a very fixed position. • They are said to be vibrating in place.

  5. II. Liquids • Atoms in a liquid are further spread out from one another. • They flow freely within the solution and are moving in a random motion.

  6. III. Gases • Atoms in a gas are in constant random motion.

  7. Least forces Most forces

  8. What are intermolecular forces?

  9. I. Intermolecular Forces • Intermolecular forces are forces that attract molecules to one another. • The three main types of intermolecular forces are: (1) Hydrogen Bonding (2) Dipole-Dipole Forces (3) Dispersion Force (also known as Van der Waals Forces)

  10. II. Dipoles • A dipoleis a separation of charge. • Molecules can have a separation of charge due to electronegativity • This causes the electrons to be held closer to the element with the higher electronegativity.

  11. Pulls electrons towards itself because it has a higher electronegativity H F δ- δ+ Partial negative charge H F This is what a dipole looks like

  12. III. Dipole-Dipole Forces • Dipole-dipole forcesrefer to the attraction between molecules that have a permanent dipole.

  13. What Dipole-Dipoles Look Like Partial negative attracted to the partial positive

  14. III. Dispersion Forces • Some molecules have an induced dipole. • Dispersion forcesare the intermolecular forces resulting from the uneven distribution of electrons and the creation of temporary dipoles. • Weakest intermolecular force

  15. But, when two H2 molecules are put next to one another, a dipole is induced because electrons rearrange themselves There is no electronegativity difference between two hydrogens, so they are non-polar and do not have a dipole

  16. What the Heck?

  17. IV. Hydrogen Bonding • Hydrogen bondingis the attraction of one molecule that contains hydrogen to another molecule. • When hydrogen is bound to N, O, or F, there is a large difference in electronegativity • Creates a partial positive and negative charge • The partial positive charge on hydrogen is attracted to N, O, or F of another molecule.

  18. Hydrogen bond between H and O

  19. V. Intermolecular Forces and Phase of Substance • The degree of intermolecular forces determines the phase of a substance. Least intermolecular forces Most intermolecular forces

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