Gen Chem 2 Midterm

Liquids and Intermolecular Forces of Attraction, Solutions & Concentration Formulas, Solids, Colligative Properties, Thermodynamics

1. All matter is made up of tiny particles.

2. These particles are in constant motion.

3. The speed of a particle is proportional to temperature.

Increased temperature means greater speed.

4. Solids, liquids, and gases differ in distances between

particles, in the freedom of motion of particles, and in

the extent to which the particles interact.

What are the Kinetic Molecular Theories of Liquids and Solids?

Solid and Liquid states are referred to as condensed phases because solid and liquid states of particles are closer together

What States of Matter are called condensed phases and why?

• Assumes both volume and shape of its container

• Expands to fill its container

• Is compressible

• Flows readily

• Diffusion within a gas occurs rapidly

What are some characteristic properties of Gas?

• Assumes the shape of the portion of the container it occupies

• Does not expand to fill its container

• Is virtually incompressible

• Flows readily

• Diffusion within a liquid occurs slowly

What are some characteristic properties of Liquid?

• Retains own shape and volume

• Does not expand to fill its container

• Is virtually incompressible

• Does not flow

• Diffusion within a solid occurs extremely slowly

What are some characteristic properties of Solid?

The distance between particles

What is the fundamental difference between states of matter?

1. The kinetic energy of the particles

2. The strength of the attractions between the particles

The state a substance is in at a particular temperature and pressure depends on what 2 antagonistic entities?

• molecules

• strong

• compounds

The attractions between _________ are not nearly as ______ as the intramolecular attractions that hold _________ together.

Intermolecular forces of attraction(IMFA)

• intriguing interactions that occur between molecules, shaping the physical and chemical properties of substances.

• forces that act between separate molecules.

• These forces arise due to the varying distribution of electrons within molecules, creating temporary imbalances of charge that induce attraction or repulsion between

  neighboring molecules.

van der Waals forces

What do you call intermolecular forces as a group?

• Dipole-dipole interactions

• Hydrogen bonding

• London dispersion forces

What are the van der Waals forces?

A pair of equal and opposite electric charges or magnetic poles of opposite sign separated especially by a small distance

What are dipoles?

London dispersion forces or dispersion forces

• forces present in all molecules, whether they are non-polar

• Electrons are in constant motion and there will be instances wherein they collect in one

  area of an atom, creating a partial negative side (Induced Dipole) which forces a partial

  positive side on the neighboring atom (Instantaneous Dipole)

• These fleeting attractions contribute to the condensation of gases into liquids and the solidification of liquids into solids.

When there is an attraction between an instantaneous dipole and an induced dipole.

When do London dispersion forces/dispersion forces occur?

Instantaneous dipole

• the term given to a molecule when a dipole of uneven charges is created very quickly and randomly in a molecule

• This causes an induced dipole

Induced dipole

• a weak attraction that results when a polar molecule induces a dipole in an atom or in a nonpolar molecule by disturbing the arrangement of electrons in the nonpolar species.

Polarizability

• The tendency of a molecule’s electron cloud to distort

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

• As this increases, the dispersion forces also become stronger

The shape of the molecule or surface area

Factor affecting the strength of London Dispersion Forces:

• Long, skinny molecules tend to have stronger

  dispersion forces than short, fat ones due to the increased _______ ____

Linear Molecule

This shape of a molecule has a larger surface area that enhances intermolecular contact and increases dispersion force

Spherical Molecule

This shape of a molecule has a smaller surface area that diminishes intermolecular contact and decreases dispersion force

Molecular weight

Factor affecting the strength of London Dispersion Forces:

• The strength of dispersion forces tends to increase with increased _________ ______.

  Ex. Larger atoms have more electrons which means a stronger attractive force when they become dipoles

Dipole-Dipole Interactions

• the attraction between molecules that have permanent dipoles

• The positive end (δ+) of one is attracted to the negative end (δ−) of the other, and vice versa.

• These forces are only important when the molecules are close to each other.

As the polarity of molecules increases, so does its dipole-dipole forces

What is the relationship of dipole-dipole forces and molecules’ polarity?

The higher the dipole-dipole force, the higher the boiling point is due to greater IMFA

What is the relationship of dipole-dipole forces and a molecule’s boiling point

Hydrogen Bonding

• Dipole-dipole interactions that arise in part from the high electronegativity of nitrogen, oxygen, and fluorine.

• Unusually strong

• When ________ is bonded to one of

  those very electronegative elements, the

  ________ nucleus is exposed.

• Due to the difference in electronegativity, it becomes difficult to separate hydrogen from

  NOF thus making water have a high boiling point.

The dipole–dipole interactions experienced when H is bonded to N, O, or F

What interactions causes hydrogen bonding

Ion-dipole interaction

• the intermolecular force of attraction between a charged ion (cation or anion) and a molecule that has a dipole

• The strength of these forces is what makes it possible for ionic substances to dissolve in polar solvents.

? Increasing interaction strenght

a. London-dispersion forces

b. Dipole-dipole forces

c. Hydrogen bonding

d. Ion-dipole bonding

e. Ion bonding

• Boiling Point and Melting Point

• Viscosity

• Surface Tension

• Capillary Action

List the Liquid Properties Affected by Intermolecular Forces

Boiling Point

• the temperature at which liquid boils

Melting Point

• the temperature at which a substance changes state from solid to liquid

The stronger the IMFA, the higher the boiling and melting point of a substance

What is the relationship of a substance’s Intermolecular force of attraction(IMFA) to its boiling & melting point?

Viscosity

• Resistance of a liquid to flow

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

• Longer Carbon Chain = Higher _________

Centipoise

What is the unit of measurement of Viscosity?

• Viscosity increases with stronger IMFA

• Viscosity decreases with higher temperature

What is the relationship of a substance’s viscosity to its Intermolecular force of attraction(IMFA) and temperature?

Surface tension

• The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of its molecules.

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

The stronger the IMFA, the greater the surface tension of a substance

What is the relationship of a substance’s Intermolecular force of attraction(IMFA) to its surface tension?

Cohesive Forces

• Intermolecular forces that bind similar molecules to one another(Mercury = Convex)

Adhesive Forces

• Intermolecular forces that bind a substance to a surface(Water = Concave)

Capillary Action

• The rise of liquids up narrow tubes

  Ex. Water has stronger adhesive forces with glass; mercury has stronger cohesive forces with itself.

• Adhesive forces attract the liquid to the wall of the tube.

• Cohesive forces attract the liquid to itself.

How are cohesive and adhesive forces important for capillary action?

Vapor pressure

• Pressure exerted by vapor onto a liquid in a container

• At any temperature, some liquid

  molecules have enough energy to escape the surface and become a gas.

The higher the vapor pressure, the weaker the intermolecular forces

How do intermolecular forces of attraction affect the vapor pressure of a liquid?

As the temperature of a substance increases its vapor pressure also increases

• As the temperature rises, the fraction of

  molecules that have enough energy to

  break free increases.

What is the relationship of a substance’s temperature to its vapor pressure?

When liquid molecules evaporate and vapor molecules condense at the same rate.

rate of vaporization = rate of condensation

When do liquid and vapor pressure reach a state of dynamic equilibrium?

The boiling point of a liquid is the temperature at which its vapor pressure equals atmospheric pressure.

Boiling point of a liquid is when vapor pressure = atmospheric pressure

Define the boiling point of a liquid in relation to temperature, vapor pressure and atmospheric pressure

The temperature at which its vapor pressure is 760 torr

What temperature is considered the normal boiling point of a liquid?

Volatility

• describes how easily a substance will vaporize (turn into a gas or vapor)

• a substance that evaporates readily at normal temperatures

• one that has a measurable vapor pressure

The more volatile, the weaker the intermolecular forces.

How do intermolecular forces of attraction affect volatility?

Solutions

• are homogeneous mixtures of two or more pure substances.

• the solute is dispersed uniformly throughout the solvent.

Solute

• the component of a solution that is lesser in quantity; the substance being dissolved.

Solvent

• the component of a solution that is greater in amount; the dissolving substance of a solution.

1. The natural tendency of substances to mix and spread into larger volumes when not restrained in some way

2. The types of intermolecular interactions involved in the solution process

The ability of substances to form solutions depends on 2 factors

• Mixing of gases is a spontaneous process.

• Each gas acts as if it is alone to fill the container.

• Mixing causes more randomness in the position of the molecules, increasing a thermodynamic quantity called entropy.

• The formation of solutions is favored by the increase in entropy that accompanies mixing.

Give the Natural Tendency towards Mixing

When molecules of different types are brought together, mixing occurs spontaneously unless the molecules are restrained wither by sufficiently strong intermolecular forces

How does IMFA affect the ability of substances to form solutions?

Solute-solute interactions

Intermolecular Interaction Involved in Solution Formation:

• interactions between solute particles must be overcome to disperse the solute particles through the solvent

Solvent-solvent interactions

Intermolecular Interaction Involved in Solution Formation:

• interactions between solvent particles must be overcome to make room for the solute particles in the solvent

Solvent-solute interactions

Intermolecular Interaction Involved in Solution Formation:

• interactions between solvent and solute particles occur as the particles mix

Solubility

• is 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 solution

• solutions where the solvent holds more solute than is normally possible at that temperature.

  • These solutions are unstable; crystallization can usually be stimulated by adding a “seed crystal” or scratching the side of the flask.

  • These are uncommon solutions.

• Solute-solvent interactions

• Pressure

• Temperature

List the factors that affect solubility

• The stronger the solute-solvent interaction, the greater the solubility of a solute in that solvent

  • The larger the gas(molar mass), the more soluble it will be in water.

• Polar organic molecules dissolve in water better than nonpolar organic molecules

  • hydrogen bonding increases solubility

What is the relationship between solute-solvent interactions and how it affects a solute’s solubility?

Miscible

• Liquids that mix in all proportions

Immiscible

• Liquids that do not mix in one another

• A solution of Hexane and water are a good example becuase hexane is nonpolar and water is polar

• External pressure has very little effect on the solubility of liquids and solids.

• In contrast, the solubility of gases increases as the partial pressure of the gas above a solution increases.

How does pressure affect the solubility of solids, liquids and gases?

If the pressure of a gas over liquid increases, the amount of gas dissolved in the liquid will increase proportionally.

How does Henry’s law explain the relationship of the pressure of gas and the solubility of solutes?

• an increase in temperature produces an increase in solubility for solids[most of the time].

• The addition of more heat facilitates the dissolving reaction by providing energy to break bonds in the solid.

How does temperature affect the solubility of a solid in a liquid?

• the solubility (concentration) increases with an increase in temperature.

• An increase in temperature puts a stress on the equilibrium condition and causes it to shift to the right. The stress is relieved because the dissolving process consumes some of the heat.

How does temperature affect the solubility of a liquid in a liquid?

as the temperature increases, solubility decreases accordingly.

How does temperature affect the solubility of a gas in a liquid?

1. Mass percentage

2. Parts per million (ppm)

3. Mole fraction

4. Molarity

5. Molality

List the Units of Solution Concentration

Give the % by weight(w/w) formula

Give the % by volume(v/v) formula

Give the % by weight by volume(w/v) formula

Give the Parts per million formula(ppm) still relating mass of a solute to the total mass of the solution

Note: Since percent is out of 100, we multiplied by 100.

Give the formula to find the moles of a component

Give the mole fraction formula

• Mole fraction is the ratio of moles of a

  substance to the total number of moles in a

  solution.

• It does not matter if it is for a solute or for a

  solvent.

Give the formula for Molarity(M)

• Molarity varies with temperature (volume

  changes).

Give the formula for Molality(m)

• Molality does not vary with temperature

  (mass does not change).

Give the Dilution Formula

Metallic solids

Type of Solid and how it they bond:

• share a network of highly delocalized electrons meaning they have free movement around the solid

• Generally created through metallic bonding

• Due to the delocalized nature of the electrons, it is a good heat and electricity conductor.

• It is also shiny due to the photoelectric effect. (Basically, the free electrons when taken in

  light release excess energy absorbed thus making the metal look reflective.)

• Has a high melting point due to the strong IMFA

• Because it is covalently bonded, when distorted it does not break easily.

Properties of Metallic Solids

Ionic Solids

Type of Solid and how it they bond:

• are sets of cations and anions mutually attracted to one another.

• Are held together by ionic bonding (difference in charges).

• Usually have structures that minimize the distance between oppositely charged and maximize the distance between like-charged

• Really hard and have high melting points due to strong IMFA

• Poor conductor when solid due to the rigid nature of the lattice

• Good conductor when liquid to the electronegative ions being mobile.

• Is brittle. This is due to the alternating structure of the solid, a slight change can cause

  like-charged particles to interact thus destroying the structure of the lattice.

Properties of Ionic Solids

Covalent-network solids

Type of Solid and how it they bond:

• are joined by an extensive network of covalent bonds.

• All atoms in the lattice are covalently bonded thus giving it a really robust structure

  • Diamonds are an example of this.

• Is hard, has a high melting point, and is a poor conductor.

• Though it is brittle, powdered forms are rarely seen due to most covalent-network solids

  being inherently small.

Properties of Covalent-Networks Solids

Molecular solids

Type of Solid and how it they bond:

• are discrete molecules that are linked to one another only by van der Waals forces.

• Graphite is the only _________ ______ to be able to conduct electricity due to the large gap in

  between the sheets allowing for easy passage of particles.

• They are soft(weak attractive forces),

• Have low melting points(weak attractive forces),

• Poor conductors(particles cannot move easily),

• Brittle(deformation cause attractive forces to be broken).

Properties of Molecular Solids

Crystalline solids

type of solids that has atoms arranged in a very regular pattern

Amorphous solids

type of solids characterized by a distinct lack of order in the arrangement of atoms.

Crystal Lattice

• the symmetrical three-dimensional structural arrangements of atoms, ions or molecules (constituent particle) inside a crystalline solid as points.

• It can be defined as the geometrical arrangement of the atoms, ions or molecules of the crystalline solid as points in space.

Lattice point

• represents each atom, molecule or ions (constituent particle) is in crystal lattices

• joined together by a straight line in a crystal lattice.

Unit Cell

• the smallest part (portion) of a crystal lattice. It is the simplest repeating unit in a crystal structure.

• The entire lattice is generated by the repetition of this in different directions.

Primitive/Simple Cubic Unit Cell

Type of Unit Cells

• points only at the corners

• Coordination Number = 6

• One above, 4 surrounding the center, and one below

• Has only 1 atom (1⁄8 atom for 8 corners)

Body Centered Unit Cell(BCC)

Type of Unit Cells

• points at corners and one at the center

• Coordination Number = 8

• 4 above and 4 below

• Has 2 atoms (1 atom at center + 1⁄8 atom for 8 corners)

Face-Centered Unit Cell(BCC)

Type of Unit Cells

• points at corners and at faces

• Coordination Number = 12

• 4 above, 4 surrounding center, 4 below

• Has 4 atoms (1⁄2 atoms for 6 faces + 1⁄8 atom for 8 corners)

1. Oblique

2. Square

3. Rectangular

4. Hexagonal

Give the names of the 2D Unit Cells

1. a ≠ b, y is arbitrary

2. a = b, y = 90°

3. a ≠ b, y = 90°

4. a = b, y = 120°

1. Cubic(PBF)

2. Tetragonal(PB)

3. Othrorhombic(PBFC)

4. Rhombohedral(P)

5. Hexagonal(P)

6. Monoclinic(PC)

7. Triclinic(P)

Give the names of the 3D Unit Cells

1. All axes are the same and are all perpendicular

2. Two axes are the same length and are all perpendicular

3. Different lengths and are all perpendicular

4. Equal lengths but no perpendicular axes

5. Partial part of a full hexagon has two axes of the same length

6. No axes have the same length and two are perpendicular

7. No axes are the same length nor are they perpendicular

Close Packing

• The atoms in a crystal pack as close together as they can based on the respective sizes of the atoms.