Chem 2 Quiz 1 (Chapter 10)

Two ideal gas assumptions

1. There’s no intermolecular forces (no interaction/attraction)

2. Gas particles don’t occupy any space (non-fixed volume)

Gas density and shape

Gas - low density, expand to fill shape of container

Liquid density and shape

Liquid - moderate density, take shape of container

Solid density and shape

Solid - high density, doesn’t take shape of the container

Liquids and solids intermolecular forces

Both have lots of IMF because they have to be strong enough to hold molecules together to stay in that phase

Intramolecular Forces

Chemical bonds between atoms in a molecule (covalent bonding)

• present in all phases

• determine chemical properties

Intermolecular forces are weak compared to ….

covalent bonds

Intermolecular forces…

are between molecules and are much weaker bonds

but… their strength determines physical properties

Types of intermolecular forces

Dipole-Dipole, (London) Dispersion, and Hydrogen Bonds

Dipole-Dipole bond

Attraction between opposite charged ends of a molecule and occur in all polar molecules

(Intermediate strength intermolecular force)

Hydrogen Bonds

An H atom bonds to a lone pair on N, O, F (those three are very electronegative and hog the Hydrogen atom - making H partially positive)

Special kind of dipole-dipole interaction and is the strongest type of dipole interaction

Strongest intermolecular force

(London) Dispersion Force

Results from the attraction of temporary dipoles created by electronic motion (moves back and forth from molecule movement = temporary weak attraction)

Found in all molecules (only force found in nonpolar molecule

Weakest intermolecular force

Gas ideal vs. real IMF

Gas ideally has no intermolecular forces

Gas really has few intermolecular forces

Liquid IMF

Has lots of intermolecular forces (they are strong)

Solid IMF

Has lots of intermolecular forces

Liquid properties

Boiling point

surface tensions

viscosity

capillary action

vapor pressure

How does intermolecular forces affect liquid boiling point

Strong inter = higher boiling point

because it takes more energy to pull these strong bonds apart

Boiling Point

Temperature at which vapor pressure of liquid is the same as atmospheric (external) pressure

How does stronger IMF affect viscosity

Makes viscosity higher - molecules are closer together, making them harder to move past one another

How does stronger IMF affect vapor pressure

Makes vapor pressure lower - molecules are tightly together making it harder for them to escape into a gas phase

How does stronger IMF affect boiling point, viscosity, vapor pressure

Higher boiling point

Higher viscosity

lower vapor pressure

Viscosity

Resistance to flow

the more intermolecular forces = higher viscosity

Which has a higher viscosity - H2O vs. C5H12

H2O is higher viscosity because of the H-bond, while C5H12 has weak bonds and is nonpolar

Which is higher in viscosity - C₂H₅OH vs. CHCl₃

C₂H₅OH has higher viscosity because it has an H-bond

Vapor Pressure

Pressure above a liquid which results from evaporation of the liquid

• depends on temperature (high temp = high vapor pressure)

• higher vapor pressure at a given temperature, the more volatile the compound (easily goes into the gas phase)

• lower IMF = higher vp

Melting

Solid → liquid

• endothermic (Delta H is positive because energy is going into it to change phases)

Vaporization

Liquid → vapor

• endothermic (Delta H is positive because energy is going into it to change phases)

Sublimation

Solid → Vapor

• endothermic (Delta H is positive because energy is going into it to change phases)

Phase Diagram

Shows where each phase exists

Critical Temperature

the highest temperature at which a substance can still exist as a liquid, no matter how much pressure you apply

Critical Pressure

the minimum pressure needed to turn a gas into a liquid at its critical temperature

Supercritical Fluid

Created when the substance is above critical temperature and critical pressure

• has properties intermediate between liquid and gas

• flows like a gas, and dissolves substances like a liquid

Solids

Ordered arrangements of atoms

• rigid

• keeps its shape

• can be crystal or glass

Crystal and Glass

Types of solid with different patterns of atoms

Crystal

Most common type of solid that has a repeating pattern of atoms

Glass

Amorphous type of solid with no repeating pattern of atoms

Types of solid crystals

Metallic

Molecular

Ionic

Covalent

Metallic Solids

Type of solid crystal with metal atoms that make up lattice

• conducts electricity

• Malleable and ductile (shapable)

• Non-directional covalent bonding (held together by forces in all directions, and electrons are free to move = shapable)

Covalent Solids

Consists of atoms bound together through covalent bonds

strong bonds

ex: diamond, graphite, sand, ceramics

pm to cm

divide by 10¹⁰

Molecular Solids

Molecules occupy the corners of the lattice

• Sugar, ice, iodine

• all IMF can be possibly found in this molecule

Ionic Solids

Ions at corners of unit cells (and it’s gaps)

• strong forces (ionic bonds) hold them together → high melting point

• don’t conduct electricity until melted or dissolved (movement of electrons)

Layered Structures (crystals)

Closest packing atoms arranged to make efficient use of space

Either hexagonal or cubic closest packed

Hexagonal Closest Packed

ababab layers

Cubic Closest Packed

abcabc layers

Unit Cell

Smallest repeating pattern for the crystal

• three types include

  • simple cubic

  • face centered cubic

  • body centered cubic

Simple Cubic

Least efficiently packed

One atom at each corner and atoms touch along the edge

1 atom per unit cell

Body centered cubic

one atom at each corner and one atom in center of unit cell

atoms touch along the body diagonal

2 atoms per unit cell

2nd most efficiently packed

Face Centered cubic

one atom at each corner and one in each face

most efficiently packed

4 atoms per unit cell