Chem 2 Chapter 12

molecules with a large surface are have ___ points of contact between them than molecules with less surface area. This leads to ___ dispersion forces overall.

more, stronger

The vapor pressure of a given molecular substance is affected by changes in ___ and by the strength of the ___ forces for the substance.

temperature, intermolecular

CH3F

dipole-dipole forces

CH3OH

hydrogen bonding

Describe the surface tension of a liquid

1. A polar liquid will have higher surface tension than a nonpolar liquid 2. Surface tension is the result of a net downward and inward force on the surface particles of a liquid 3. Surface tension is the amount of energy required to increase the surface area of a liquid by a unit area

Describe the relationship between the intermolecular forces of a molecular substance and its boiling point?

1. A substance with strong intermolecular forces will require more energy to separate the molecules so that they can enter the vapor phase. 2. A substance with weak intermolecular forces will have a low boiling point.

Describe melting and melting point

1. At melting point of a substance the solid and liquid phases are in equilibrium. 2. Pressure changes have little effect on the melting point of a substance.

H2O exhibits extremely strong and efficient hydrogen bonding between its molecules. What is the result of this behavior?

1. High capillarity 2. High specific heat capacity 3. High surface tension

Describe equilibrium

1. If the rate of condensation is equal to the rate of evaporation, a phase equilibrium exists. 2. At equilibrium, the amount of the substance in each phase remains constant. 3. A system must be closed in order for a phase equilibrium to be established.

What is the relationship between dispersion forces and particle size?

1. Large particles are more polarizable and experience stronger dispersion forces. 2. For molecules of similar shape, dispersion forces tend to increase with increasing molar mass

How does polarizability affect intermolecular forces?

A more polarized molecule experiences stronger dispersion forces and therefore stronger intermolecular forces overall

Describe a heating cooling curve

A plot of heat vs. temperature for a substance that is heated or cooled at a constant rate and constant pressure.

Gas to Liquid

Condensation

True or False: A bond between O and H within any molecule is called a hydrogen bond

False

Liquid to Solid

Freezing

Face-centered cubic

Identical particles lie at each corner and in the center of each face but not in the center of the cube

Metallic

Soft to hard, varying melting points, excellent conductors of electricity ad heat as well as malleable and ductile

What does the term doping refer to in semiconductors?

The addition of a small amount of a Group 3A or Group 5A element to a semiconductor sample

Insulator

The energy gap between the valence and conduction bands is large and no current can flow

In cubic closest packing

The particles of the third layer do not lie directly over the particles of the first layer

Describe packing efficiency of a unit cell

The percentage of the total volume occupied by the particles themselves

Conductor

There is no energy gap between the valence and conduction bands so electrons flow freely

Describe polarizability

This is a measure of how the electron cloud around an atom responds to its electronic environment.

Diamond is one of the common crystalline forms of ___ in which each atom is bonded to 4 others by strong, ___ bonds to create a large 3-D array.

carbon, silicon covalent

Describe the relationship between intermolecular forces and the vapor pressure of a substance.

a substance with weaker intermolecular forces vaporizes more easily and has a high vapor pressure.

The hexagonal close-packed structure has the pattern

ababab

The cubic-packed structure has the pattern

abcabc

Ionic solid

cations and anions arranged in a regular lattice held together by ion-ion attraction

The number of nearest neighbors for a particle in the unit cell of a crystal is called the ___ number of particles

coordination

A change in the physical state of a molecular substance does NOT involve the breaking of

covalent bonds

Compounds that maintain an orderly arrangement of particles in the liquid phase are known as liquid __

crystals

C3H8

dispersion forces

Covalent bonds are classified as

Intramolecular forces

CaCl2

ionic bonding

A physical state of matter that is chemically and physically uniform is called a(n)

phase

For a molecular substance, the ___ energy in the form of intermolecular forces tends to draw molecules together. The __ energy associated with the movement of the molecules tends to disperse them. The relative strength of these two effects determines the behavior of the phase of matter.

potential, kinetic

Energy of movement is low compared to the attraction between particles; particles remain fixed in position relative to each other.

solid

The liquid and ___ states are called the ___states of matter because their particles are very close together.

solid, condensed

What are typical properties of ceramics?

strength, thermal insulation, hardness

The ___pattern of H bonding in H2O gives ice a very open structure with large ___ between the molecules. Water therefore differs from most liquids because it becomes ___ dense when it freezes.

tetrahedral, spaces, less

Network Covalent

very hard with high melting points but usually poor thermal and electrical conductors.

Given the following information, what is the enthalpy change when 54.5 g of water vapor is heated from 100.0C to 200.0C (C(gas)=33.1J/mol*K and Delta H(vap) =40.7 kJ/mol)

+1.00 * 10^4 J 54.5g*1mol/18.02 q=3.02*33.1*100

Calculate the enthalpy change when 1.75 moles of diethyl ether changes from the liquid to the gas phase if Delta H(vap)=27.3 kJ/mol and C(liquid)=172 J/mol*K for this substance

+47.8 kJ The sign must be positive because the process is endothermic

Describe the critical temperature and pressure of a substance

1. At the critical point of a substance, the densities of the liquid and gas are equal 2. At temperature and pressures above the critical point a substance exists as a supercritical fluid

What is a modern application of a liquid crystal?

1. Calculator and watch displays 2. High -strength materials 3. Color changing thermometers

Describe the three types of cubic unit cells

1. Each particle in a simple cubic unit cell has a coordination number of 6 2. The face-centered cubic cell has no particles in the center of the cube 3. The body-centered cubic unit cell has 2 atoms per unit cell

Describe the different packing arrangements observed for cubic unit cells?

1. In hexagonal closest packing, the particles of the third layer lie directly over the particles of the first layer. 2. The cubic close-packed structure has the repeating pattern abcabc 3. Cubic closest packing is based on the face-centered cubic cell

which structures would allow a molecular substance to exhibit hydrogen bonding between molecules?

1. One or more O-H bonds 2. One or more N-H bonds

Describe the general trends in polarizabilty

1. Polarizability increases down a group on the periodic table 2. Anions are larger than their parent atoms and are therefore more polarizable 3. The greater the number of electrons a particle has, the greater its polarizability will generally be.

What is needed to calculate the numerical change in vapor pressure with change in temperature

1. R= 8.314 J/K*mol 2. One or both of the vapor pressures 3. Delta H(vap)

Describe the boiling point of a substance

1. The boiling point is the temperature at which the vapor pressure equals the external pressure. 2. The boiling point of a substance increases as the external pressure increases. 3. Boiling occurs when the vapor pressure of the liquid is sufficient for bubbles of vapor to form in the interior of the liquid.

Describe the bonding in graphite

1. The pi bonds in graphite are delocalized, allowing graphite to conduct electricity. 2. Graphite consists of flat sheets or layers of carbon atoms that are covalently bonded together with the sheet.

Describe viscosity of a liquid

1. Viscosity is a liquids resistance to flow 2. A liquid with stronger intermolecuar forces will have a higher viscosity 3. The viscosity of a given liquid decreases with increasing temperature

Describe sublimation

1. nonpolar molecular substances are more likely to sublime than polar substances. 2. The tendency of a molecular substance to sublime is related to the strength of its intermolecular forces. 3. Sublimation is the change from the solid directly to the gas phase

Nano-structural crystal

Consist of materials that do not behave as atoms or as crystals; sizes range from 1 to 100 nm

Polymeric crystal

Consists of extremely large molecules that adopt the shape of coils due to intermolecular forces.

Ceramic crystal

Consists of mostly covalent solids formed at high temperature that are very resistant to heat and chemicals

Gas to Solid

Deposition

Delta H(vap)

Liquid to Gas

Delta H(subl)

Solid to Gas

Delta H(fus)

Solid to Liquid

Simple cubic

The centers of eight identical particles define the corners of a cube

Semiconductor

The energy gap between the valence and conduction bands is small so electrons can cross if thermally excited.

Intermolecular forces

The forces of attraction between one individual molecule and another.

Liquid to Gas

Vaporization

Network covalent solid

atoms held together by covalent bonds

Adhesive forces

attractive forces between the liquid and the particles of the container

All___ are nonmetallic inorganic compounds.

ceramics

Within a phase, a change in heat causes the temperature of the substance to ___ as the ___ energy of the molecules changes. During a phase change, however, a change in heat causes a change in the ___ energy of the molecules and the temperature will___.

change, kinetic, potential, stay the same

The electrons of a smaller atom or ion are___ the nucleus and held ___ tightly than those of a larger atom or ion. A smaller atom or ion is therefore___ polarized than a larger one.

closer to, more, less

A liquid rises against the pull of gravity through a narrow space through capillary action. This results from a competition between ___ intermolecular forces between the molecules of the liquid itself and the ___ forces between the liquid and the walls of the container.

cohesive; adhesive

Liquid crystal

consist of a crystal phase that flows like a liquid but has an ordered shape

Bonding forces include ionic bonds, metallic bonds, and ___ bonds. These types of forces are much ___ than the forces of attraction between individual molecules, which are called ___ forces.

covalent, stronger, intermolecular

Solids that have well defined shapes due to the orderly arrangement of their particles are called ___ solids, whereas solids whose particles lack orderly placement and therefore have poorly defined shapes are ___ solids

crystalline, amorphous

A p-type semiconductor is formed by doping silicon with any Group 3A element. This ___the number of valence electrons available, creating___sites into which Si electrons can migrate. This increases the conductivity of the material.

decreases, positive

The attraction between an ion and a nearby polar molecule is called an ion-___interaction. This attraction force is important when a(n)___ compound dissolves in a polar solvent such as H2O

dipole, ionic

p-type

doped with a group 3A element

n-type

doped with a group 5A element

Luster

electrons absorb and release photons as they move between the valence and conduction bands

If a liquid is placed in a closed container, molecules with sufficient ___will move from the liquid to the gas phase. Gas phase molecules will in turn condense. Eventually the ___ of evaporation and condensation will be equal and the system is said to have reached phase___.

energy, rates, equilibrium

The boiling point of a substance is the temperature at which the vapor pressure of the substance is ___ the external pressure; hence the boiling point depends on the applied pressure.

equal to

The phase changes of many substances are reversible and a phase change, just like a chemical reaction, may reach ___providing it takes place in a(n)___system.

equilibrium, closed

Molecular

fairly soft with low melting points, poor conduction of heat and electricity

True or False: Dispersion forces are exhibited only by nonpolar molecules.

false

Energy of motion is high compared to the attraction between particles; particles are far apart.

gas

The surface tension of a liquid will be ___ for a liquid with stronger forces of attraction between its particles.

greater

The larger a molecule or atom, the ___ the number of electrons and the ___ polarized it will generally be. The strength of the dispersion forces for a particular substance therefore generally ___ as molar mass increases, providing molecules of similar shape are compared.

greater, more, increases

Ionic

hard and brittle with high melting points, good thermal and electrical conductivity in the molten phase.

Since H2O is able to exhibit different types of intermolecular forces including hydrogen bonding, this substance has a ___ heat capacity and a ___ heat of vaporization compared to other liquids.

high; high

Atomic solid

individual atoms held together by dispersion forces

Cohesive forces

intermolecular forces within the liquid itself

The melting point of a substance is the temperature at which the particles have enough ___ energy to break free from the ___ phase and enter the ___ phase.

kinetic, solid, liquid

The particles in a crystal are arranged in an orderly 3-D array called the crystal ___. The simplest repeating unit of the crystal is called the unit___.

lattice, cell

Unlike most other substances, the density of solid H2O is___ than the density of the liquid; hence water ___ when it freezes. This is reflected in the phase diagram for H2O. The solid-liquid boundary line has a negative slope, reflecting the fact that the higher the pressure the ___ the temperature at which the water freezes.

less, expands, lower

The forces of attraction between particles are appreciable; fixed volume; freedom of movement allows fluidity.

liquid

At ___ temperature the forces of attraction between particles dominate because the particles are moving slowly. At ___ temperatures the movement of the particles overcomes the attractions.

lower, higher

When two polar molecules are close to each other they will orient themselves so that the positive pole of one molecule attracts the ___ pole on the adjacent molecule. These intermolecular forces are called ___ - ___ forces.

negative, dipole-dipole

When hydrogen is covalently bonded to ___, oxygen, or fluorine there will be an attraction between such a hydrogen and a(n) ___ pair of electrons on a nitrogen, oxygen, or fluorine atom on an adjacent molecule. This attraction is called a(n) ___ bond and it is strongest type of intermolecular force between neutral species.

nitrogen, lone, hydrogen

Dispersion forces are the only type on intermolecular force exhibited by atoms and by ___ molecules. Without the existence of dispersion forces, such substances could not exist in the ___ states of matter.

nonpolar, condensed

The triple point is represented on a phase diagram to show when all three ___of a substance are at ___

phases, equilibrium

Malleability

positive metal ions can move past each other protected by the repulsion of the delocalized electrons

a 25.0g sample of ice at -6.5C is removed from the freezer and allowed to warm until it melts. Given the data below, what reflects the calculations needed to determine the total heat change for this process. Melting point at 1atm=0.0C; c(solid)=2.09J/g*degreesC; DeltaH(fus)=6.02 kJ/mol

q for the phase change is given by 1.39*6.02=8.37kJ 25g*1mol/18.02g=1.39mol and q=nDeltaH(fus)=1.39*6.02=8.37 The total heat change for the process is equal to +8.71kJ q1=25.0*2.09*6.5=340J or 0.34kJ and q2=1.39*6.05=8.37kJ

Which equation should be used to calculate the heat change when a given molar amount of H2O is heated from 15C to 95C

q=n C deltaT

Thermal conductivity

the highest energy electrons are excited by heat and the energy is transferred as kinetic energy

Electrical conductivity

the highest energy electrons are excited into empty orbitals allowing them to move readily through a sample

In hexagonal closest packing

the particles of the third layer lie directly over the particles of the first layer

True or False: A compound containing one or more oxygen atoms is not necessarily capable of forming hydrogen bonds between its molecules.

true

The pressure exerted by the ___ above a liquid is called the equilibrium ___ pressure. This pressure ___ as the temperature of the system increases.

vapor, vapor. increases

Describe bonding and intermolecular forces

1. Bonding forces are generally much stronger than intermolecular forces. 2. For a molecular substance, the strength of the intermolecular forces determines the physical properties of its phases. 2. Intermolecular forces involve partial or small charges that are far apart and are relatively weak.

Describe van der Waals radi

1. The van der waals radius for a given atom is larger than its covalent radius 2. The van der Waals distance and radius are important for determining how closely and two molecules can approach each other. 3. In general, van der waals radii increase down a group in the periodic table

Describe vapor pressure

1. Vapor pressure increases as temperature increases. 2. The vapor pressure is the pressure exerted by the vapor above a liquid at equilibrium. 3. The vapor pressure of a molecular substance depends on the strength of its intermolecular forces.

How does the addition of phosphorus to silicon create an n-type semiconductor?

The extra electrons from the phosphorus atoms bridge the gap between the valence and conductance bands, increasing conductivity.

The physical state of a molecular substance at a particular temperature and pressure depends on the strength of its

Intermolecular forces

- Delta H(fus)

Liquid to Solid

Solid to Liquid

Melting/Fusion

Solid to Gas

Sublimation

Body-centered cubic

Identical particles lie at each corner and in the center of the cube

All particles experience ___ forces, a weak attraction that results from induced electron cloud distortion. These forces increase the overall attraction between particles. The more polarized a particle, the ___ this effect will be.

dispersion, greater

An increase in the temperature of a substance will___ the fraction of molecules that have enough kinetic energy to escape the liquid phase and will therefore cause a(n)___in vapor pressure.

increase, increase

If the external pressure on a liquid is increased, the vapor pressure of the liquid must___ in order for the liquid to boil. The molecules of the liquid require___ kinetic energy so that more of them can escape the liquid phase. The boiling point of the liquid is therefore ___ when the external pressure is increased.

increase, more, higher

Molecular solid

individual molecules held together by various combinations of intermolecular forces

A momentary change in the electron density surrounding an atom or a molecule causes it to have a(n)___ dipole even if it is not normally polar. This induces a similar effect in a nearby molecule or atom and there will be a weak attraction between the two particles as a result. These weak interactions are called ___ forces or London forces.

instantaneous, dispersion

What is the relationship between molecular shape and the strength of dispersion forces?

molecules with a large surface area have more points of contact and therefore experience stronger dispersion forces.