3B5 Effects of Bonding, Structure, and Interparticle Interactions Flashcards
Relate bonding, structure, and intermolecular forces to physical properties like boiling point and solubility.
How do intermolecular forces affect physical properties of substances?
They influence:
- Melting points
- Boiling points
- Freezing points
- Viscosity
- Surface tension
- Solubility
Define:
boiling point
The temperature at which a liquid’s vapor pressure equals the external pressure, causing it to transition into a gas.
The boiling point depends on atmospheric pressure; it decreases at higher altitudes due to lower pressure.
What factor primarily determines boiling point?
The strength of intermolecular forces.
Stronger forces, such as hydrogen bonds, require more energy to overcome, leading to higher boiling points.
Which has stronger intermolecular forces:
covalent or hydrogen
Covalent bonds
Covalent bonds involve shared electrons between atoms, making them stronger than intermolecular hydrogen bonds.
Define:
melting point
The temperature at which a substance transitions from solid to liquid.
Melting point is influenced by the lattice energy in crystalline solids and the strength of intermolecular forces.
Fill in the blank:
A molecule with stronger intermolecular forces will have a _______ melting point.
higher
Substances like ionic solids have high melting points due to strong ionic interactions.
Define:
vapor pressure
The pressure exerted by a vapor in equilibrium with its liquid or solid phase.
Which factors affect vapor pressure?
- Temperature
- Intermolecular forces
Vapor pressure increases with temperature as more molecules gain energy to escape into the gas phase.
Weaker intermolecular forces make it easier for molecules to vaporize.
True or False:
Ionic compounds are soluble in water.
True
The solubility depends on:
- The compound’s lattice energy and the hydration energy provided by water.
- The ion’s size and charge density; smaller ions tend to dissolve more easily.
What type of solvent dissolves polar solutes?
Polar solvents.
Water is a common polar solvent; it dissolves salts and polar organic compounds like alcohols.
Which bond type contributes most to water’s high boiling point?
Hydrogen bonds
These bonds occur between water molecules, leading to high boiling and melting points compared to similar-sized molecules.
What is the relationship between molecular weight and boiling point?
Generally, higher molecular weight increases boiling point, assuming similar intermolecular forces.
Larger molecules have more electrons, leading to stronger London dispersion forces.
Larger electron clouds are more polarizable, increasing temporary dipole interactions.
Fill in the blank:
Molecules with _______ intermolecular forces have higher equilibrium vapor pressures.
weaker
Substances like ether have high vapor pressures due to weak intermolecular forces.
Fill in the blank:
Compounds with _______ intermolecular forces evaporate faster.
weaker
Volatile compounds, like acetone, evaporate quickly due to weak intermolecular forces.
True or False:
Smaller ions generally have lower melting and boiling points.
False
Smaller ions allow stronger electrostatic interactions due to higher charge density.
Why do ionic solids have high melting points?
Due to the strong electrostatic forces between ions in the lattice.
For example, NaCl has a high melting point due to strong ionic interactions.
Which has a higher boiling point:
NaCl or H₂O
NaCl
NaCl has ionic bonds which are much stronger than the hydrogen bonds in water.
Fill in the blank:
Nonpolar molecules dissolve best in _______ solvents.
nonpolar
Solvents like hexane dissolve nonpolar compounds, such as oils.
Why is ethanol soluble in water?
Due to hydrogen bonding between ethanol and water molecules.
Ethanol’s O-H group allows it to form strong interactions with water.
What type of compound is likely to have the lowest melting point?
Nonpolar molecular compounds with weak London dispersion forces.
Examples include simple hydrocarbons like methane and ethane.
What does ‘like dissolves like’ mean?
- Polar solvents dissolve polar solutes.
- Nonpolar solvents dissolve nonpolar solutes.
This principle explains the immiscibility of oil and water.
Which has a higher boiling point:
water (H₂O) or methane (CH₄)
Water (H₂O)
Water has stronger hydrogen bonding that requires more energy to overcome.
Methane, being nonpolar, exhibits only weak London dispersion forces.
Which has a higher boiling point:
HF or HCl
HF
HF has stronger hydrogen bonding.
HCl exhibits dipole-dipole interactions but lacks hydrogen bonding.
Which has a higher boiling point:
H₂S or H₂O
H₂O
H₂S only exhibits dipole-dipole interactions, which are weaker than hydrogen bonds in H₂O.
Why do metals generally have high melting points?
Due to strong metallic bonds formed by a sea of delocalized electrons.
Metals like tungsten have very high melting points due to their bonding strength.
True or False:
Increasing pressure increases boiling point.
True
A higher external pressure requires more energy to match vapor pressure.
Why does ice float on water?
Ice has a lower density due to hydrogen-bonded open lattice structure.
This structure increases the volume of ice, making it less dense than liquid water.
What property of water allows it to dissolve ionic compounds?
Water’s polarity and ability to form hydration shells around ions.
Water’s partial charges interact with cations and anions, stabilizing them in solution.
Why does water have a high surface tension?
Due to hydrogen bonding that causes water molecules to stick together at the surface.
Which force is responsible for water’s high heat of vaporization?
Hydrogen bonding.
Hydrogen bonds require significant energy to break.
Why are noble gases able to liquefy at low temperatures?
Due to London dispersion forces between their atoms.
These are the only forces acting between noble gas atoms.
Why do alcohols have higher boiling points than alkanes of similar molecular weight?
Alcohols exhibit hydrogen bonding, whereas alkanes rely only on weaker London forces.
Hydrogen bonding requires more energy to break.
What is the role of hydrogen bonds in molecular interactions?
They cause close packing of molecules in a substance.
This is particularly evident in the behavior of liquids and solids.
Why are hydrogen bonds important in biological systems?
- They stabilize structures like DNA and proteins.
- They contribute to the properties of water, a life essential.
Hydrogen bonding is crucial for maintaining the double helix structure of DNA.
