3B4 Interparticle Interactions Flashcards
Explain different types of interparticle interactions, including London forces, dipole-dipole, dipole-induced, and hydrogen bonding.
Define:
intermolecular forces
The attraction that exists between molecules, ions, and atoms when they are in close proximity.
Intermolecular interactions occur when molecules, ions, or atoms are oppositely charged and close enough.
Which type of intermolecular force is the weakest?
London forces
These forces are weak because they are based on temporary dipoles.
Other types of intermolecular forces include dipole-dipole interactions and hydrogen bonding.
Which is the strongest type of intermolecular force?
Hydrogen bond
Hydrogen bonds occur between a slightly positive hydrogen on one molecule and a slightly negative atom, such as F, O, or N.
What is the difference between intermolecular and intramolecular forces?
- Intermolecular forces: They exist between molecules.
- Intramolecular forces: They hold a molecule together.
Intermolecular forces pull different molecules together; intramolecular forces maintain a single molecule.
What distinguishes polar and nonpolar molecules?
Polar molecules have a constant dipole; nonpolar molecules do not.
Example of nonpolar molecules: H₂, N₂, Cl₂, and F₂.
Define:
Van der Waals forces
A collective name for:
- London dispersion forces
- Dipole-dipole attractions
These forces arise from the ability of particles to polarize and be polarized.
Define:
a dipole
An atom or molecule with positive and negative ends.
Example: Hydrogen fluoride molecule has a dipole due to differing electronegativities of hydrogen and fluorine.
Define:
London forces
Weak instantaneous induced dipole-dipole attractions that occur between all atoms and molecules, regardless of polarity.
Named after Fritz London, who described this phenomenon in 1930.
Nonpolar molecules rely solely on London forces.
What is the role of temporary dipoles in London forces?
They are responsible for instantaneous attractions.
These interactions are short-lived but constant.
Why are London forces also called dispersion forces?
They arise from the dispersion of electrons within molecules or atoms, leading to temporary dipoles.
These forces are ubiquitous and weak.
What causes London dispersion forces?
The motion of electrons producing instantaneous dipoles in nonpolar molecules.
Instantaneous dipoles can polarize adjacent nonpolar particles.
What factors influence the strength of London dispersion forces?
- Atomic size or molecular mass.
- Molecular shape.
Larger and more elongated molecules typically exhibit stronger dispersion forces.
Define:
polarizability
The ease with which the electron cloud of an atom or molecule can be distorted to form a temporary dipole.
Polarization is the process of distorting the electron cloud of a particle.
Larger atoms/molecules are more polarizable.
How do molecular shapes affect London dispersion forces?
Cylindrical structures have more contact points than spherical structures, leading to stronger dispersion forces.
Example: n-pentane has a higher boiling point than neopentane due to its shape.
How do you identify London dispersion forces?
Identify if a substance is nonpolar; if it is, it exhibits only London dispersion forces.
All substances have London dispersion forces, but they are the only forces in nonpolar substances.
Why do linear molecules have stronger London forces than spherical ones?
Linear molecules have more surface area for interactions, leading to stronger London forces.
What is the primary intermolecular force in noble gases?
London dispersion forces
Noble gases are nonpolar and exhibit weak forces due to their small size and lack of dipoles.
What causes dipole-dipole interactions?
The electrostatic attraction between the positive end of one polar molecule and the negative end of another.
These forces are often the result of electrons being unequally distributed among the atoms in a compound.
These forces are stronger in highly polar molecules.
Fill in the blank:
______ molecules experience dipole-dipole interactions.
Polar
Dipole-dipole interactions require a permanent dipole.
List two examples of molecules that exhibit dipole-dipole interactions.
- Hydrogen chloride (HCl)
- Water (H₂O)
These molecules are polar, allowing dipole-dipole attractions.
Why do polar molecules have stronger interparticle interactions than nonpolar molecules?
Polar molecules exhibit dipole-dipole forces in addition to London forces, leading to stronger overall interactions.
Nonpolar molecules rely only on weaker London forces.
What is a dipole-induced dipole interaction?
An interaction that occurs when a polar molecule induces a dipole in a nonpolar molecule, resulting in an attraction.
Polar molecules induce temporary dipoles in nonpolar molecules.
These interactions are weaker than dipole-dipole forces.
What is an ion-dipole interaction?
An interaction involving one neutral molecule with a dipole and one ion engaged in electrostatic interaction.
A dipole has two oppositely charged poles, one positive and one negative.
What is the relative strength of ion-dipole interactions compared to others?
Ion-dipole interactions are fairly weak but stronger than dipole-dipole forces.
They require the ion and polar molecule to be in closer proximity than hydrogen bonds.
Which type of force acts between polar molecules and ions in solution?
Ion-dipole interactions
These interactions are critical for dissolving ionic compounds in polar solvents.
What are the main factors influencing the strength of dipole-induced dipole interactions?
- The polarizability of the nonpolar molecule.
- The dipole moment of the polar molecule.
Higher polarizability increases interaction strength.
Why is hydrogen bonding stronger than dipole-dipole interactions?
Hydrogen bonds involve a partial sharing of electrons and a highly polarized bond between hydrogen and highly electronegative atoms like N, O, or F.
The small size of hydrogen allows close approach, increasing strength.
List three molecules that exhibit hydrogen bonding.
- Water (H₂O)
- Ammonia (NH₃)
- Hydrogen fluoride (HF)
All involve hydrogen bonded to N, O, or F.
True or False:
Hydrogen bonding occurs only in polar molecules.
True
Hydrogen bonding requires a polar bond between hydrogen and N, O, or F.
N, O, and F atoms are highly electronegative, creating the necessary polarization.
What determines the strength of hydrogen bonding?
- The electronegativity of the atom bonded to hydrogen.
- The proximity of the interacting molecules.
Higher electronegativity leads to stronger hydrogen bonds.
What is the relative strength of dipole-dipole interactions compared to hydrogen bonding?
Dipole-dipole interactions are weaker than hydrogen bonding.
Hydrogen bonding involves partial electron sharing, increasing strength.
What kind of intermolecular forces do alcohols exhibit?
- Hydrogen bonding
- Dipole-dipole interactions
- London dispersion forces
Alcohols form hydrogen bonds due to the O-H group, making them soluble in water.
Which has stronger intermolecular forces:
NH₃ or CH₄
NH₃
NH₃ has stronger forces due to hydrogen bonding.
CH₄ only exhibits London dispersion forces.
