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Lecture 4.1 – 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 4.1 – 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. • 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.
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)
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
III. Dipole-Dipole Forces • Dipole-dipole forcesrefer to the attraction between molecules that have a permanent dipole.
What Dipole-Dipoles Look Like Partial negative attracted to the partial positive
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
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
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.
V. Intermolecular Forces and Phase of Substance • The degree of intermolecular forces determines the phase of a substance. Least intermolecular forces Most intermolecular forces