AP Chemistry:: Intermolecular Forces Properties

What is an INTERMOLECULAR FORCE, and how does it fundamentally differ from an INTRAMOLECULAR bond (like a covalent or ionic bond)?

- **A)** An intermolecular force is an attractive force acting BETWEEN separate molecules (or particles), typically much WEAKER than an intramolecular bond, which is the strong force holding atoms TOGETHER WITHIN a single molecule or compound
- **B)** Intermolecular forces are always STRONGER than intramolecular bonds, the reverse of the actual typical relationship
- **C)** This concept has no actual relationship to distinguishing forces acting within a molecule from forces acting between separate molecules
- **D)** Intermolecular forces and intramolecular bonds refer to exactly the SAME concept, with no meaningful distinction between forces acting within versus between molecules

What is a LONDON DISPERSION FORCE (also called a van der Waals force), and in which molecules is it present?

- **A)** London dispersion forces are present ONLY in polar molecules, with no actual presence in nonpolar molecules or atoms
- **B)** This type of force has no actual relationship to temporary, fluctuating electron distributions within a molecule
- **C)** A WEAK, temporary attractive force arising from randomly fluctuating electron distributions creating brief, temporary dipoles; London dispersion forces are present in ALL molecules and atoms, including nonpolar ones
- **D)** London dispersion forces are always the STRONGEST type of intermolecular force, stronger than hydrogen bonding in every case

How does MOLECULAR SIZE (or more precisely, the number of electrons in a molecule) generally affect the STRENGTH of LONDON DISPERSION FORCES between molecules of a similar type?

- **A)** LARGER molecules with MORE electrons always experience WEAKER London dispersion forces, the reverse of the actual general relationship
- **B)** London dispersion force strength depends only on a molecule's overall SHAPE, with electron count playing no actual role
- **C)** Molecular size has no actual relationship to the strength of London dispersion forces between molecules
- **D)** LARGER molecules (with MORE electrons) generally experience STRONGER London dispersion forces, since there are more electrons available to create larger, more significant temporary dipole fluctuations

What is a DIPOLE-DIPOLE FORCE, and in which type of molecules is this intermolecular force present?

- **A)** Dipole-dipole forces are present in ALL molecules, including nonpolar ones, with no actual requirement for molecular polarity
- **B)** An attractive force between the PARTIAL POSITIVE end of one POLAR molecule and the PARTIAL NEGATIVE end of a NEARBY polar molecule; dipole-dipole forces are present specifically in POLAR molecules (which have a permanent dipole moment)
- **C)** This type of force has no actual relationship to the attraction between partially charged ends of polar molecules
- **D)** Dipole-dipole forces only occur between a POSITIVE end of one molecule and another POSITIVE end of a nearby molecule (rather than opposite charges attracting)

How does the STRENGTH of a typical DIPOLE-DIPOLE force generally compare to the strength of a typical LONDON DISPERSION force between molecules of similar size?

- **A)** This comparison has no actual relationship between dipole-dipole forces and London dispersion forces of similarly-sized molecules
- **B)** Dipole-dipole forces are always WEAKER than London dispersion forces between similarly-sized molecules, the reverse of the actual general relationship
- **C)** Dipole-dipole forces are generally STRONGER than London dispersion forces between molecules of similar size, since dipole-dipole forces arise from PERMANENT (rather than temporary/fluctuating) charge separations
- **D)** Dipole-dipole forces and London dispersion forces are always exactly EQUAL in strength, with no meaningful distinction between them

What is HYDROGEN BONDING, and what THREE specific types of atoms must be involved for this particularly strong type of intermolecular force to occur?

- **A)** Hydrogen bonding can occur between a hydrogen atom and ANY other atom in the periodic table, with no specific requirement for nitrogen, oxygen, or fluorine
- **B)** This type of force has no actual relationship to a hydrogen atom's interaction with highly electronegative atoms like nitrogen, oxygen, or fluorine
- **C)** Hydrogen bonding is always WEAKER than a typical dipole-dipole force, rather than being unusually strong among intermolecular forces
- **D)** A particularly STRONG type of dipole-dipole interaction that occurs specifically when a HYDROGEN atom (bonded to a highly electronegative atom) is attracted to a LONE PAIR on a NEARBY highly electronegative atom -- specifically NITROGEN, OXYGEN, or FLUORINE

Why does WATER (H2O) have an UNUSUALLY HIGH boiling point compared to other similarly-sized molecules (like H2S) that do NOT exhibit hydrogen bonding?

- **A)** Water's high boiling point has no actual relationship to hydrogen bonding between its molecules
- **B)** Water and H2S experience EXACTLY the same type and strength of intermolecular forces, making their different boiling points unexplainable by intermolecular force differences
- **C)** Water's OXYGEN atom is highly electronegative and its hydrogens are directly bonded to that oxygen, allowing EXTENSIVE HYDROGEN BONDING between water molecules -- this significantly stronger intermolecular force requires much MORE energy to overcome during boiling, unlike H2S (sulfur is less electronegative, no hydrogen bonding)
- **D)** H2S actually exhibits STRONGER hydrogen bonding than water, which would predict H2S should have the higher boiling point (the reverse of the actual observation)

What is VISCOSITY, as a physical property of a liquid, and how does the STRENGTH of a liquid's intermolecular forces generally relate to its viscosity?

- **A)** Viscosity refers to a liquid's BOILING POINT, rather than its resistance to flow
- **B)** This concept has no actual relationship between intermolecular force strength and a liquid's resistance to flow
- **C)** Liquids with STRONGER intermolecular forces always have LOWER viscosity, the reverse of the actual general relationship
- **D)** Viscosity is a liquid's RESISTANCE to FLOW; liquids with STRONGER intermolecular forces between their molecules generally have HIGHER viscosity, since those molecules resist sliding past one another more strongly