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Questions and Answers
The attractive force called the London dispersion force is one of the three types of ______ forces.
The attractive force called the London dispersion force is one of the three types of ______ forces.
van der Waals
The dispersion force is named in honor of physicist Fritz ______.
The dispersion force is named in honor of physicist Fritz ______.
London
Dispersion forces become significant only when molecules are very ______.
Dispersion forces become significant only when molecules are very ______.
close
Larger and heavier atoms exhibit stronger dispersion forces than ______ atoms.
Larger and heavier atoms exhibit stronger dispersion forces than ______ atoms.
In a polar molecule like hydrogen chloride, the Cl atom bears a partial ______ charge.
In a polar molecule like hydrogen chloride, the Cl atom bears a partial ______ charge.
Dipole-dipole attractions occur due to the attraction between the positive end of one molecule and the negative end of another, such as in ______.
Dipole-dipole attractions occur due to the attraction between the positive end of one molecule and the negative end of another, such as in ______.
Nonpolar molecules such as F2 do not have a permanent ______ charge separation.
Nonpolar molecules such as F2 do not have a permanent ______ charge separation.
When comparing HCl to nonpolar molecules, both substances have approximately the same molecular ______.
When comparing HCl to nonpolar molecules, both substances have approximately the same molecular ______.
HCl has a higher normal boiling point of ______ K compared to F2 which is ______ K.
HCl has a higher normal boiling point of ______ K compared to F2 which is ______ K.
The attractions between HCl molecules are known as - attractions.
The attractions between HCl molecules are known as - attractions.
Water (H2O) has a lower molecular mass of ______ amu than nitrosyl fluoride (ONF), which has a mass of ______ amu.
Water (H2O) has a lower molecular mass of ______ amu than nitrosyl fluoride (ONF), which has a mass of ______ amu.
Hydrogen bonding is a particularly strong type of - attraction.
Hydrogen bonding is a particularly strong type of - attraction.
Molecules with ______-H, O-H, or N-H moieties experience strong hydrogen bonding.
Molecules with ______-H, O-H, or N-H moieties experience strong hydrogen bonding.
Hydrogen bonds are about ______ to ______% as strong as covalent bonds.
Hydrogen bonds are about ______ to ______% as strong as covalent bonds.
The weaker dispersion forces between nonpolar F2 molecules are insufficient to keep them in a ______ state.
The weaker dispersion forces between nonpolar F2 molecules are insufficient to keep them in a ______ state.
The large difference in boiling points between H2O and ONF cannot solely be attributed to ______ forces.
The large difference in boiling points between H2O and ONF cannot solely be attributed to ______ forces.
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Study Notes
Dispersion Forces
- One of the three types of van der Waals forces, present in all condensed phases.
- Named after physicist Fritz London, who explained the forces in 1928.
- Also known as London dispersion forces or simply dispersion forces.
- Atoms and molecules can develop temporary dipoles due to the constant motion of electrons.
- Temporary dipoles can induce dipoles in neighboring atoms or molecules, leading to attractive forces.
- These forces are relatively weak and significant only at close distances.
- Larger, heavier atoms and molecules exhibit stronger dispersion forces.
- Example: F2 and Cl2 are gases at room temperature; Br2 is a liquid; I2 is a solid, reflecting varying strengths of dispersion forces.
Dipole-Dipole Attractions
- Occur between polar molecules, which have distinct partial positive and negative charges.
- Example: In hydrogen chloride (HCl), Cl has a partial negative charge, while H has a partial positive charge.
- The attraction between the positive end of one HCl molecule and the negative end of another leads to dipole-dipole attraction.
- Comparison of HCl and nonpolar F2 demonstrates that dipole-dipole attractions create stronger intermolecular forces than dispersion forces.
- Both HCl and F2 can have similar properties (number of atoms and molecular mass), but boiling points differ significantly: HCl has a boiling point of 188 K, and F2 is 85 K.
- The strength of dipole-dipole attractions correlates with boiling points, freezing points, and enthalpies of vaporization or fusion.
Hydrogen Bonding
- Occurs in polar molecules with hydrogen atoms bonded to highly electronegative elements (F, O, N).
- Example: Nitrosyl fluoride (ONF) is a gas at room temperature, while water (H2O) is a liquid despite having a lower molecular mass.
- The disparity in boiling points between ONF and H2O is not due to dispersion forces or dipole moments but rather to hydrogen bonding.
- Hydrogen bonds arise from the significant electronegativity difference between hydrogen and the bonding electronegative atom (F, O, or N).
- Characterized by highly concentrated partial charges and strong intermolecular attractions.
- Hydrogen bonds, despite being termed "bonds," are intermolecular forces, significantly weaker than covalent bonds (5-10% as strong) but stronger than typical dipole-dipole attractions and dispersion forces.
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