Chem 2 Midterms Reviewer

States of matter

The fundamental difference between _____ is the distance between particles.

Distance between particles

The fundamental difference between states of matter

1. Kinetic energy of the particles

2. Strength of attractions between particles

The state a substance is in at a particular temperature and pressure depends on two antagonistic entities:

1. Temperature

2. Pressure

The state a substance is in at a particular (1) and (2) depends on two antagonistic entities:

1. Kinetic energy of the particles

2. Strength of attractions between particles

Intermolecular forces

• Weaker than intramolecular forces

• They are strong enough to control physical properties such as:

  • boiling point

  • melting point

  • vapor pressure

  • viscosities

• As a group, they are referred to as van der Waals forces

Van der Waals forces

Intermolecular forces as a group

1. Dipole-dipole interactions

2. Hydrogen bonding

3. London dispersion forces

H o L D

The 3 van der Waals forces

London dispersion forces

• van der Waals force

• a.k.a. dispersion forces

• Attractions between an instantaneous dipole and an induced dipole

• Present in all molecules, ignoring polarity

Polarizability

• The tendency of an electron cloud to distort

• The tendency of molecules to generate induced electric dipole moments when subjected to an electric field

1. Shape of the molecule

2. Molecular weight

The 2 factors that affect dispersion forces

1. Stronger

2. Increased surface area

Long, skinny molecules (e.g., n-pentane) tend to have (1) dispersion forces because of (2)

Directly proportional

• ⬆ Molecular weight = ⬆ Dispersion forces

Larger atoms have larger electron clouds, easier to polarize

• The relationship between molecular weight and dispersion forces

• Why?

Dipole-dipole interactions

• van der Waals force

• Molecules that have permanent _____ are attracted to each other

• The positive end (δ⁺) of a molecule is attracted to the negative end (δ^-) of the other

• Only important when the molecules are close to each other

1. Polarity

2. Directly proportional

1. A factor that affects dipole-dipole interactions

2. The relationship of this factor to dipole-dipole interactions

Hydrogen bonding

• van der Waals force

• The dipole-dipole interactions experienced when _____ is bonded to N, O or F are unusually strong

• Arises in part from the high electronegativity of N, O and F

• The _____ nucleus is exposed

Ion-dipole interactions

• Not a van der Waals force

• Important in solutions of _____

• Its strength makes it possible for _____ substances to dissolve in polar solvents

1. London dispersion forces

2. Dipole-dipole interactions

3. Hydrogen bonding

4. Ion-dipole forces

5. Ionic bonding

LD HI I

Increasing order of IMFA

1. Boiling point

2. Melting point

3. Viscosity

4. Surface tension

5. Capillary action

5 liquid properties affected by IMFA

Boiling point

• Liquid property affected by IMFA

• The temperature at which a liquid boils

• The temperature at which its vapor pressure equals the atmospheric pressure

Melting point

• Liquid property affected by IMFA

• The temperature at which it changes state from solid to liquid

Directly proportional

The relationship between the boiling and melting points of a substance with its IMFA

Viscosity

• Liquid property affected by IMFA

• Resistance of a liquid to flow

• Related to the ease with which molecules can move past each other

1. Directly proportional

2. Inversely proportional

1. The relationship of viscosity to IMFA

2. The relationship of viscosity and temperature

Surface tension

• Liquid property affected by IMFA

• Water acts as if it has a “skin” on it due to extra inward forces on its surface

Cohesive forces

IMFA that bind similar molecules to one another (e.g., H₂O < Hg)

Adhesive forces

IMFA that bind a substance to a surface (e.g., H₂O > Hg)

Capillary action

• Liquid property affected by IMFA

• The rise of liquids up narrow tubes

• Adhesion + cohesion

Vapor pressure

At any temperature, some liquid molecules have enough energy to escape the surface and become gas

Directly proportional

The relationship of vapor pressure and temperature

Directly proportional

The relationship of vapor pressure and pressure

Inversely proportional

The relationship of vapor pressure and IMFA

Volatility

A substance’s degree to transition from a liquid/solid state to a gaseous state under specific temperature and pressure conditions

Inversely proportional

The relationship of volatility and IMFA

Normal boiling point

The temperature at which its vapor pressure is 760 torr or 1 atm

1. Metallic

2. Ionic

3. Covalent-network

4. Molecular

MMIC

4 general types of solids

Crystalline solids

Atoms in solids that are arranged in a very regular pattern

Amorphous solids

Atoms in solids that have a distinct lack of order in their arrangement

1. Crystal lattices

2. Unit cells/tiles

1. One can deduce the pattern in a crystalline solid by thinking of the substance as a (1) of repeating shapes formed by the atoms in the crystal

2. The individual shapes of the (1) form (2) that must fill the entire space of the substance

1. Cubic

2. Tetragonal

3. Orthorhombic

4. Rhombohedral

5. Hexagonal

6. Monoclinic

7. Triclinic

CORTT H&M

7 basic 3D lattices

Close packing

The atoms in a crystal _____ as close together as they can based on the respective sizes of the atom

(Metal) Alloys

Combinations of 2 or more elements, mostly metals

1. Substitutional alloy

2. Interstitial alloy

2 types of metal alloys

Substitutional alloy

• Type of metal alloy

• A 2nd element takes the place of a metal atom

Interstitial alloy

• Type of metal alloy

• A 2nd element fills a space in the lattice of metal atoms

Metallic bonding

• Bond between metals

• Form large groups of atoms that share electrons among them

  • Metal = a group of cations suspended in a sea of electrons

1. Dense

2. High melting point

3. Good electrical conductor

4. Good heat conductor

5. Malleable

6. Ductile

7. Lustrous

DED HM LM

7 properties of metallic solids

Ionic solids

• Type of solid

• The lattice comprises of alternately charged ions

• Quintessential crystals

1. Opposite

2. Like

The different sized-ions in an ionic compound minimize the distance between (1) charged ions while keeping (2)-charged ions away from each other

1. Hard

2. Melting point

3. Poor electrical conductor (solid)

4. Good electrical conductor (molten)

5. Brittle

BEHM

5 properties of ionic solids

Diamonds

Example of a covalent-network solid

1. Hard

2. Melting point, very high

3. Poor heat conductor

4. Poor electrical conductor

5. Brittle

5 properties of covalent-network solids

Molecular solid

A solid whose atoms are held together by van der Waals forces

Graphite

Example of molecular solid

1. Soft

2. Low melting point

3. Poor electrical conductor

4. Poor heat conductor

5. Brittle

SL PPB

5 properties of molecular solids

Phase change

Each state of matter can transform into either of the other two states

Heat of fusion

The energy required to change a solid at its melting point to a liquid

Heat of vaporization

The energy required to change a liquid at its boiling point to a gas

Heat of sublimation

The energy required to change a solid directly to a gas

Heat

The _____ added to the system at melting and boiling points goes into pulling the molecules farther apart from each other

Temperature

The _____ of the substance does not rise during a phase change

Phase diagrams

Display the state of a substance at various pressures and temperatures and the places where equilibria exist between phases

1. Triple point (T)

2. Critical point (C)

The liquid-vapor interface starts at the (1), at which all 3 states are in equilibrium, and ends at the (2), above which the liquid and vapor are indistinguishable from each other

Liquid crystals

• Some substances don’t go directly from the solid state to the liquid state

• They have some traits of both solids and liquids

• Molecules have some degree of order

1. Nematic

2. Smectic

3. Cholesteryl

3 types of liquid crystals

Nematic liquid crystal

• Type of liquid crystal

• Molecules are only ordered in one dimension along the long axis

Smectic liquid crystals

• Type of liquid crystal

• Molecules are ordered into two dimensions along the long axis and in layers

Cholesteryl liquid crystals

• Type of liquid crystal

• Nematic-like crystals are layered at angles to each other

Solutions

Homogenous mixtures of two or more pure substances

1. Solute

2. Solvent

In a solution, the (1) is dispersed uniformly throughout the (2)

1. Natural tendency toward mixing

2. Intermolecular forces

The ability of substances to form solutions depends on

Spontaneous

Mixing of gases is a _____ process

1. Mixing

2. Entropy

(1) causes more randomness in the position of the molecules, increasing a thermodynamic quantity called (2)

Entropy

The formation of solutions is favored by the increase in _____ that accompanies mixing

1. Solute-solute

2. Solvent-solvent

3. Solvent-solute

Attractions formed when forming a solution

Solute-solute interactions

• Attraction formed when forming a solution

• Must be overcome to disperse these particles when making a solution

Solvent-solvent interactions

• Attraction formed when forming a solution

• Must be overcome to make room for the solute

Solvent-solute interactions

• Attraction formed when forming a solution

• Occur as the particles mix

Solubility

The maximum amount of solute that can dissolve in a given amount of solvent at a given temperature

Saturated solutions

Solutions that have the maximum amount of solute dissolved

Unsaturated solutions

Solutions that have any amount of solute less than the maximum amount dissolved in solution

Supersaturated solutions

• The solvent of a solution holds more solute than is normally possible at that temperature

• Unstable

• Crystallization can usually be stimulated by adding “seed crystal” or scratching the side of the flask

• Uncommon

1. Solute-solvent interactions

2. Pressure

3. Temperature

3 factors that affect solubility

Directly proportional

The relationship of solute-solvent interaction and solubility of a solute in that solvent

1. N2

2. O2

3. Ar

4. Kr

4 gases that only exhibit dispersion force

Directly proportional

The relationship of the size of a gas and its solubility in water

1. Polar

2. Nonpolar

(1) organic molecules dissolve in water better than (2) organic molecules

Hydrogen bonding

_____ increases solubility, since C—C and C—H bonds aren’t very polar

Miscible

Liquids that mix in all proportions are _____

Immiscible

Liquids that don’t mix in one another are _____

1. Solids

2. Liquids

The solubility of (1) and (2) aren’t appreciably affected by pressure

Henry’s Law

According to _____, the solubility of a gas is proportional to the partial pressure of the gas above the solution

Directly proportional

The relationship of most solids’ solubility and temperature

1. Unsaturation

2. Supersaturation

GRAPH Below the curve indicates (1) while above the curve indicates (2)

Inversely proportional

The relationship of gases’ solubility and the temperature

1. Mass percentage

2. Parts per million

3. Mole fraction

4. Molarity

5. Molality

5 units of concentration

• % weight = (mass of solute / mass of solution)(100)

• w/w

• Mass percentage formula

• Unit

• % weight by volume = (mass of solute / volume of solution)(100)

• w/v

• Percent weight by volume formula

• Unit

ppm = (mass of component in a solution / total mass of solution)(10^6)

Parts per million formula

mole fraction = moles of a component / moles of the solution

Mole fraction formula

Colligative properties

They depend only on the quantity, not the identity of the solute particles