Chem 1320 1st Edition Lecture 38Outline of Last Lecture I. How to ΔHII. Intermolecular ForcesOutline of Current LectureI. Nonbonding forcesII. Phase DiagramsCurrent Lecture I. Non-Bonding ForcesWhat they are not: covalent interactions - Nonbonding interactions (forces) are electrostatic and described by Coulomb’s law1. Ion-dipole forces: - Strong nonbonding interactions - Trends: increasing strength of interaction. It increases the change of the ion and increases with bond polarity or larger dipole moments 2. Dipole- dipole forces- Trends: the strength increases with bond polarity. Larger dipole moments will have larger interactions 3. Hydrogen bond- Special type of dipole- dipole interactions- When: it is bonded covalently to an especially electronegative atom N, O, or F. the hydrogen orients to point at a region of larger electron density. - It is small molecules can get close together and H-O, H-N and N-F bonds are especiallypolar. 4. Change- induced dipole forces- electrons are mobile and can respond to nearby charges.Polarizability: how easy it is to deform an electron cloudThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Trends: mass of the atom or molecule increases polarizability (more mass more protons so more electrons too) and atoms left to right on Ion- induced dipole: the periodic table polarizability decreases due to increased Zeff (the tighter the electrons are held, the harder it is to shift them around.) Dipole- induced dipole: weaken the interaction because they might not have a permanent dipole movement. 5. Dispersion forces (London Forces)- Even without dipole movements or changes being present a nonpolar compound can be polarized- At any instant the elections will not be equally distributed in an atom or molecule- Temporary unequal distribution can polarize other nearby species - Trends: as mass increases so does the number of electrons. More electrons means more polarizability, so stronger dispersion interactions and increases size or length at a molecule will increase dispersion interactions- Dispersion reactions are always present even in polar molecules. - The interactions are relatively weak but have an additive effect. - About 80% of the interactions between H-Cl are due to dispersion forcesII. Phase Diagrams- Most substances will have a similar set of relationships between phases.- Triple point- where three phases coexist - Critical point- where the gas and liquid become indistinguishable - No phase change occurs at a temperature above the critical point once the correct pressure is
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