AP Chem Ch 10

Question 0

Exceptions to octet rule

Answer 0

B, Be, and Al (as a non-metal) are stable with 6 or 4 electrons
N is often stable with 7 electrons
P and larger atoms are often stable with 10 or 12 electrons

Question 1

Method for Lewis Dot Structure

Answer 1

1. Add up valence electrons
2. Re count valence electrons
3. Arrange atoms. Least electronegative atom in the center
4. Use pairs of electrons to draw in single bonds
5. Put the rest of the electrons on the non central atoms trying to form octets
6. Put extra electrons on central atom
7. Check if central atom has octet
8. Form double/triple bonds to give central atom an octet

Question 2

Formal charge

Answer 2

valence e- - #bonded electrons/2 - # of electrons in a lone pair

Ex. Oxygen in a double bond:
6-4/2-4

Question 3

London dispersion forces

Answer 3

Induced/temporary dipole
Increases with size–larger the molecule, bigger the LDF
Type of IMF for non-polar molecules
As you go down a group, freezing and boiling points increase because bigger LDF. Stronger IMF allows for this increase

Question 4

Polarizability

Answer 4

The freezing point rises going down the group. Principle reason for this is because as the atomic number goes up, number of electrons GO up, so there is an increased chance of the occurrence of momentary dipole interactions. We describe this phenomenon using the term polarizability, which indicates the ease with which the electron cloud of an atom can be distorted to give a dipolar charge distribution. Thus we say that large atoms with many electrons exhibit a higher polarizability than small atoms. So, LDF increases as size increases

Question 5

Dipole-Dipole

Answer 5

Molecules with a permanent dipole (polar species) desire to align to reduce repulsions. More favorable–less energy required–when a polar molecule interacts with another polar molecule.

Question 6

H-bonding

Answer 6

Extreme case of dipole-dipole where Hydrogen is attracted to a lone pair in an N, O, or F atom.
Very strong IMF because of the big electronegativity difference–strong polar bond between H-N, H-O, H-F
Also occurs because the dipoles are able to closely approach one another because hydrogen is so small.

Question 7

Effects of hydrogen bonding

Answer 7

Since the IMF is so strong, higher boiling and melting points, less vapor pressure than dipole-dipole or LDF species

Question 8

Why do polar molecules mix with polar molecules and not with non-polar molecules?

Answer 8

Polar– dipole produced with a partial positive and a partial negative side. Attracted to other polar molecules where partial positive is attracted to partial negative because this is a favorable reaction, can just bond, doesn’t take too much energy
However, this partially charged molecule won’t interact with a non-charged non-polar molecule unless a lot of energy is induced, so this is not favorable

Question 9

Surface tension

Answer 9

The resistance of a liquid to an increase in its surface area. Liquids with large IMFS have high surface tension.

Question 10

Capillary action

Answer 10

Spontaneous rising of a liquid in a narrow tube.
Caused by 2 different types of forces:
1. Cohesive forces– IMF among the molecules of the liquid
2. Adhesive forces– forces between liquid and container
Adhesive forces occur when the container is made of a substance with polar bonds so the water can attract to it.
The ability of water to wet the glass makes it creep up the walls of the tube where the water surface touches the glass. Increases the surface area of the water, which is opposed by the cohesive forces trying to minimize the surface. So, with the strong adhesive and cohesive forces, water pulls itself up a glass capillary tube to a height where the weight of the column of water just balances the water’s tendency to be attracted to the glass surface.

Question 11

Cohesive vs adhesive forces

Answer 11

Cohesive among molecules of a liquid

Adhesive with liquid and the container

Question 12

Concave vs convex meniscus and reason why

Answer 12

Polar has a concave meniscus because of strong adhesive forces.
Attracted to the glass
Nonpolar is convex because of strong cohesive forces. Won’t interact with the polar glass tube.

Question 13

Viscosity

Answer 13

Measure of the resistance to flow.
Larger IMFS have larger viscosities
Also more sticky with higher viscoscities

Question 14

Solid vs gas vs liquid

Answer 14

Solid is rigid structures with essentially no molecular motions
Gas has lots of motion. No IMFs
Liquid the hardest to analyze because of both motion and IMFS

Question 15

X - ray diffraction

Answer 15

Diffraction occurs when beams of light are scattered from a regular array of points in which the spacing between the components are comparable with the wavelength of the light.
Allows for structure of crystalline solid to be determined

Question 16

Constructive vs destructive interference

Answer 16

Constructive when the waves of parallel beams are in phase. Produces a spot on the detector
Destructive when the waves are out of phase. No image produced.

Question 17

Importance of diffraction

Answer 17

Allows for bond lengths to be determined from the Bragg eq

Question 18

Bragg equation

Answer 18

n (lambda) = 2d * sin (theta)
n is an integer
Lambda is the wavelength
d is the disfrace between points
Theta is the angle of incident light

Question 19

Example of Bragg equation
If the wavelength of an Al crystal is 1.54 * 10^-10 m and it produces reflection at an angle of 19.3 degrees and we assume n=1, calculate the distance between the planes of atoms producing this reflection

Answer 19

Use Bragg equation:
1(1.54*10^-10)=2dsin(19.3)
d = 2.33 * 10^-10 m

Question 20

Molecular orbital theory for metals

Answer 20

Bonding in most metals is both strong and nondirectional because they are durable and have high melting points.
Electron sea model explains how there is a regular array of metal cations in a sea of valence electrons. Mobile electrons can conduct heat and electricity and the metal ions can be easily moved around as the metal is hammered into a sheet or pulled into a wire
A related model with more detailed view of the electron energies and motions is the band model, or molecular orbital model, for metals. In this model, the electrons are assumed to travel around the metal crystal in molecular orbitals formed from the valence atomic orbitals of the metal atoms. Large number of resulting molecular orbitals are closely spaced and finally form a virtual continuum of levels, called bands.

Question 21

How does temperature affect conductivity of a metal?

Answer 21

T up, so more collisions, so less conductivity.

Question 22

Band theory to explain metals conducting

Answer 22

Conduct electricity and heat very efficiently because of the availability of highly mobile electrons. Electrons in partially filled bonds are mobile, so they can flow and create charge. The molecular orbitals occupied by these conducting electrons are called conduction bands. These account for the efficiency of the conduction of heat thru metals. When one end of a metal rod is heated, the mobile electrons can rapidly transmit the thermal energy to the other end.

Question 23

Which has a bigger gap between conductive and valence band?

Answer 23

Insulator bigger gap than semiconductor

Question 24

Closest packing

Answer 24

The structure in crystalline solid materials. Packing uniform hard spheres in a manner that most efficiently uses the available space.

Question 25

Aba arrangement

Answer 25

Hexagonal closest packed (hcp) -- hexagonal unit cell. Third layer lies directly over the first because of dimples between first and second, and second and third layers.

Question 26

ABC arrangement

Answer 26

Cubic closest packed (ccp) structure. Face centered cubic unit cell. Fourth layer is like the first. Abcabc FCC has 4 atoms in 1 unit cell. And one side you can do by the diagnaol, and then pi that, so d^2 + d^2 = (4r)^2

Question 27

Simple cubic, body-centered cubic, face centered cubic

Answer 27

SC-- 1 atom per unit cell. 2r= one side BCC-- 2 atoms in a unit cell. FCC-- 4 atoms in a unit cell. One side = 4r/SQRT2

Question 28

Ex. Silver crystallizes in a CCP structure. Radius is 144 pm | Find the density of solid silver

Answer 28

CCP structure, so 4 atoms in a unit, so (4r)^2 = d^2 + d^2 d = 144*SQRT 8 = 407 pm Volume = side cubed = 6.74*10^7 pm^3 * 1/10^30 cm^3 = 6.74*10^-23 cm^3 Mass--we know that there are four atoms--> 107.9 g/mol * 1 mol/6.02*10^23 afoms * 4 afoms = 7.17*10^-22 g Mass / volume = 10.6 grams per cubic cm

Question 29

Substitutional alloy

Answer 29

When a metal has equal in size secondary metal. Host atoms are replaced by other metal atoms of similar size Brass, sterling silver

Question 30

Interstitial alloy

Answer 30

Some holes in the closest packed metal structure are occupied by small atoms, most of the time, carbon. Changes properties and makes it stronger

Question 31

Network solids

Answer 31

Many atomic solids contain strong directional covalent bonds to form a solid that might best be viewed as a giant molecule. Brittle, do not efficiently conduct heat or electricity. Carbon-- diamond, graphite Silicon-- silicates, silica Big networks of Si and O

Question 32

Ionic solids

Answer 32

``` Metal and nonmetal Ionic bonds Latrice High boiling and melting points because of high electrostatic attraction Very soluble in aqueous solution ```

Question 33

Molecular solid

Answer 33

Water Covalent bonds but really IMFS holding together the structure, hence the weak structure and lower boiling and melting points. Molecular structure, not formula units

Question 34

Semiconductor

Answer 34

Silicon is a semiconductor--a few electrons can cross the gap between the filled and empty molecular orbitals at 25 Celsius, making silicon a semiconducting element, or a semiconductor. Additionally, at higher temperatures, when more energy is available to excite electrons into the conduction bands, the conductivity of silicon increases. Typical for semiconductor, contrast to that of metals, whose conductivity decreases with increasing temperature.

Question 35

p-type semiconductor

Answer 35

Positive. Species introduced with fewer electrons than host to increase conductivity. Creates holes--absensce of an electron. Emory orbital. Holes are places of net positive charge

Question 36

p-type semiconductor

Answer 36

Positive. Species introduced with fewer electrons than host to increase conductivity. Creates holes--absensce of an electron. Emory orbital. Holes are places of net positive charge

Question 37

P-n junction

Answer 37

Where p and n semiconductors meet

Question 38

P-n junction

Answer 38

Where p and n semiconductors meet

Question 39

What happens when p and n type semiconductors are next to each other with no battery?

Answer 39

Electrons migrate from the n type to the p type by filling in the holes. Leaves the n type with holes and a net positive charge and the p type with extra electrons and net negative charge. Further migration of electrons is prevented--charge buildup results in stop of migration-- contact potential

Question 40

What happens when p and n type semiconductors are next to each other with no battery?

Answer 40

Electrons migrate from the n type to the p type by filling in the holes. Leaves the n type with holes and a net positive charge and the p type with extra electrons and net negative charge. Further migration of electrons is prevented--charge buildup results in stop of migration-- contact potential

Question 41

What happens if we put the negative end of a battery by a p-type semiconductor and the positive end by the n-type

Answer 41

Then, electrons in the n-type are drawn toward the positive terminal. Holes in the p-type towards the negative terminal Electrons don't flow across the junction Reverse bias No current flow

Question 42

What happens if we put the negative end of a battery by a p-type semiconductor and the positive end by the n-type

Answer 42

Then, electrons in the n-type are drawn toward the positive terminal. Holes in the p-type towards the negative terminal Electrons don't flow across the junction Reverse bias No current flow

Question 43

What happens when positive end of battery placed by p-type and negative by n-type?

Answer 43

The electrons in the n-type are drawn toward the positive terminal but must flow across the junction filling the holes in the p type. Holes move towards the negative terminal Forward bias Results in current flow Movement of holes and electrons is favorable. Important for circuits

Question 44

What happens when positive end of battery placed by p-type and negative by n-type?

Answer 44

The electrons in the n-type are drawn toward the positive terminal but must flow across the junction filling the holes in the p type. Holes move towards the negative terminal Forward bias Results in current flow Movement of holes and electrons is favorable. Important for circuits

Question 45

Rectifiers

Answer 45

Devices that produce a pulsating direct current from an alternating current because current only flows in forward bias.

Question 46

Rectifiers

Answer 46

Devices that produce a pulsating direct current from an alternating current because current only flows in forward bias.

Question 47

Dc vs ac

Answer 47

D.C. In one direction | AC in both directions

Question 48

Dc vs ac

Answer 48

D.C. In one direction | AC in both directions

Question 49

What happens when water is placed in a eurleymeyer flask?

Answer 49

Initially, some water evaporates/vaporizes into has but then some gas turns back into liquid-->condensation. Process continues back and forth until equilibrium reached, when the rate of the forward reaction= rate of the reverse reaction

Question 50

Equilibrium

Answer 50

When the rage of vaporization = raye of condensation | Dynamic process but no net change

Question 51

Vapor pressure

Answer 51

The pressure of the vapor present at equilibrium Patm = Pvapor + P Hg column Pvap= Patm-P Hg

Question 52

Rates of evaporation and consenation in a closed container

Answer 52

As time goes on, rate of evaporation remains constant the whole time but rage of condensation increases until the rates are equal Because it starts off with more liquid to gas, but then gas to liquid rises until equal. No net change

Question 53

Heat of vaporization

Answer 53

The energy required to vaporize 1 mol of a liquid at 1 atm | Requires energy, endothermic, because energy is needed to overcome IMFS

Question 54

How does temperature influence vapor pressure?

Answer 54

Increases significantly with temperature. To overcome the IMFS in a liquid, a molecule must have sufficient kinetic energy. As the temperature is increases, the fraction of molecules having the minimum energy needed to overcome these forces and escape to the vapor phase increases markedly. Thus the vapor pressure of a liquid increases dramatically with temperature.

Question 55

How do IMFS relate to vapor pressure?

Answer 55

Inversely proportional Liquids with large IMFS have low vapor pressures because the molecules need high energies to escape to the vapor phase. Strong H-bond in water causes it to have a low vapor pressure. For non-polar, more massive have less vapor pressures because with the extra electrons, it is more polarizable, and has bigger ldfs

Question 56

Temperature and vapor pressure equation

Answer 56

We can make a linear relation plotting ln(Pvap) vs 1/T (1/Kelvin) ln(Pvap) = -heat of vap/R (1/T) + C

Question 57

Slope of ln(Pvap) vs 1/T graph

Answer 57

Slope is - heat of vaporization / R, | So the steeper slope will have the larger heat of vaporization

Question 58

Practice problem: Vapor pressure of water at 25 degrees Celsius is 23.8 torr, delta H vap = 43.9 kJ/mol Calculate vapor pressure of water at 65 degrees Celsius

Answer 58

At 25 degrees, ln(23.8)=-43.9/8.314*10^-3 (1/298) + c C= 20.89 Now plug into same equation at 65 degrees ln(Pvap) = -43.9/8.314*10^-3 (1/338) + 20.89 Pvap = 194.4 torr

Question 59

Hearing curve for water

Answer 59

Plot of temperature vs heat added at a constant rate First starts out as a solid, temp increases to the melting point, then remains constant as melts, then increases to the boiling point, then remains constant as it vaporizes, then increases as a gas

Question 60

Phase change

Answer 60

Alters physical properties, not chemical | Involves IMFS, not bonds

Question 61

Enthalpy of fusion

Answer 61

Enthalpy change that happens at the melting point

Question 62

Solid and liquid water vapor pressure graph vs temperature

Answer 62

Melting and boiling points for a substance determined by the vapor pressures of the solid and liquid states. Below 0 degrees, solid has lower vapor pressure but above 0 degrees, solid has larger vapor pressure. At 0 degrees they are equal. So, the solid vapor pressure has a larger slope--increases more rapidly for a given rise in temperature

Question 63

Case 1: a temperature at which the vapor pressure of the solid is greater than that of the liquid

Answer 63

The solid requires a higher pressure than the liquid does to be in equilibrium with the vapor. So, as the vapor is released from the solid to try to achieve equivilibrium, the liquid will absorb vapor to try to reduce the vapor pressure to its eq value. Net effect is a conversation from solid to liquid thru the vapor phase. No solid can exist under these conditions. Solid decreases as volume of liquid rises until there is only liquid and it will come to eq with the water vapor. No further changes. Must be above the melting point

Question 64

Case 2: when the temperature is such that the vapor pressure of the solid is less than that of the liquid

Answer 64

Here, the liquid requires a higher pressure to be in equilibrium with its vapor phase. So, the liquid will gradually disappear as the solid increases. Only solid will remain. Must be below melting point.

Question 65

Case 3: temperature at which the vapor pressure of the solid = vapor pressure of the liquid

Answer 65

Here, they have the same vapor pressure, so they can coexist at eq simultaneously with the vapor. This is the freezing point. Both states coexist.

Question 66

Normal melting point

Answer 66

The temperature at which the solid and liquid states have the same vapor pressure under conditions where the total pressure = 1 Atm

Question 67

Normal boiling point

Answer 67

Boiling occurs when the vapor pressure of a liquid equals the pressure of its environment. Normal boiling point is the temperature when the vapor pressure of the liquid = 1 atm Boiling point lowers as altitude increases

Question 68

Supercool

Answer 68

Water can be supercooled--it can be cooled below 0 degrees Celsius at 1 atm pressure and remain in liquid state. Supercooling occurs because as it is coooled, the water may not achieve the degree of organization necessary to form ice at 0 degrees, and continues to exist as liquid. At some point, the correct ordering occurs and ice forms, releasing energy and bringing the temperature back up to the melting point, where the remainder of the water freezes

Question 69

Superheat

Answer 69

When a liquid is raised to temperatures above its boiling point

Question 70

Phase diagram

Answer 70

A convenient way of representing the phases of a substance as a function of temperature and pressure.

Question 71

Exp 1: what happens to ice at -20 degrees, p=1 ATM, as it is heated

Answer 71

Solid to liquid at 0 degrees and then at 100 degrees becomes vapor

Question 72

Exp 2: when ice is heated from -20 degrees at a very low pressure of 2 torr

Answer 72

Sublimation because vapor pressure of ice is equal to external pressure. Because the vapor pressure of liquid water is greater than 2 torr, it cannot exist at this pressure

Question 73

Exp 3: low pressure of 4.58 torr, ice heated from -20 degrees

Answer 73

No new phase until T = .01 Celsius | Triple point--all 3 states of matter co exist in a closed system. Solid and liquid states have same VP of 4.85 torr

Question 74

Exp 4: liquid water at 300 degrees Celsius and pressure at 225 atm

Answer 74

High ester all pressure, water can be a liquid. As temperature increases, liquid changes into a vapor thru a fluid phase -- neither liquid nor vapor

Question 75

Critical temperature

Answer 75

The temperature above which the vapor cannot be liquefied, regardless of pressure

Question 76

Critical pressure

Answer 76

The pressure required to produce liquefaction at the critical temperature

Question 77

Critical point

Answer 77

Cortical temperature and critical pressure Liquid/vapor line ends at this point. Because transition from one state to another involves the intermediate fluid region above this point

Question 78

N-type semiconductor

Answer 78

Negative | Increase conductivity by doping it with atoms with more valence electrons than the host

Question 79

Why does the solid/liquid line for water have a negative slope?

Answer 79

The melting point of ice decreases as the external pressure increases. This occurs because the density of ice is less than that of liquid water at the melting point. The maximum density of water occurs at 4 degrees Celsius, when liquid water freezes, its volume increases. Normally, this line is positive because solid density greater than liquid

Question 80

How does altitude influence cooking and boiling?

Answer 80

At higher altitude, water boils at a lower temperature, so takes longer to cook because not as much energy in the system

Question 81

What happens with water when not in a closed system?

Answer 81

In dry climates (low humidity), snow and ice seem to sublime Ice in the natural environment is not a closed system. So the pressure is produced by the atmosphere, not the solid piston. So, the vapor produced over the ice can escape from the immediate region as soon as its formed. The vapor does not come to eq with the solid, and the ice slowly dissapeads. Sublimation, which seems forbidden by the phase diagram, does in fact occur under these conditions, although it is not the sublimation under eq conditions described by the phase diagram

Question 82

Carbon dioxide phase diagram

Answer 82

Solid/liquid line has a positive slope since solid CO2 is more dense than liquid. Triple point at 5.1 atm and -56.6 Celsius Critical point at 72.8 atm and 31 degrees Celsius. At 1 atm, solid carbon dioxide sublimes at -78 degrees Celsius, a property that leads to its name, dry ice.

Question 83

Carbon dioxide in fire extinguisher

Answer 83

Exists as liquid at 25 clecius under high pressure. Liquid released from extinguisher changes into a vapor immediately. Heavier than air, smothers the fire by keeping oxygen away from the flame. Endothermic reaction, so cooling also results, helping put out the fire.