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Chem 1300 > Chapter 4 > Flashcards

Chapter 4 Flashcards

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1
Q

Electromagnetic radiation

A

composed of perpendicular oscillating waves (electric field and magnetic field)
ex) light

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2
Q

Electromagnetic spectrum: frequency and wavelength

A

order from left to right:
frequency decreases
wavelength increases

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3
Q

Electromagnetic spectrum: order of energies

A

order from left to right:

gamma rays, x rays, ultra-violet, visible light, infrared, microwaves, radio waves, long radio waves

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4
Q

Electromagnetic spectrum: order of visible light colours

A

order from left to right:

purple, blue, green, yellow, orange, red

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5
Q

How would you make a light bulb more intense? (brighter)

A

increase the amplitude of the wavelength

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6
Q

Explain the photoelectric effect.

A

Light is shined on a metal surface, where this surface absorbs the photon and its energy is transferred to an electron. Some of the energy is used to overcome the binding energy, and the rest of the energy becomes kinetic energy of the ejected electron.

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7
Q

Threshold frequency

A

energy required to eject electrons from their ground state ( metal surface )

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8
Q

True or False? Light has wave like properties but no particle like properties.

A

False. It has both

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9
Q

Photons

A

packets of energy

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10
Q

True or False? Electrons are only ejected if the frequency of light is high enough, it is not dependent on the intensity of light.

A

true.

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11
Q

Absorption and emission spectra: color vs black

A

colour: wavelengths of light that were emitted
black: wavelengths of light that were absorbed

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12
Q

Absorption and emission spectra: energy level diagram explanation

A

As photons are absorbed, it goes from the ground state to the excited state (jumps up levels).
As photons are emitted, it goes from the excited state to the ground state (goes down levels), generating heat loss.

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13
Q

Principle quantum number (n)

A

energy levels that electrons occupy and the distance electrons are from the nucleus

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14
Q

Principle quantum number (n) vs radius of orbitals vs energy of electron vs potential energy vs stability vs distance from nucleus vs number of nodes

A 
as n increases:
energy of electron increases
potential energy decreases
orbitals get larger
less stable
distance from nucleus increases
number of nodes increases
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15
Q

True or False. Electrons have wave like properties.

A

True. This suggests that every moving object has a wavelength associated with it.

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16
Q

If electrons have wave-like properties, what is the consequence of this?

A

the position of electrons cannot be precisely defined

delocalized

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17
Q

Period vs group in periodic table

A

period: same number of atomic orbitals
group: same number of valence electrons

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18
Q

Azimuthal quantum number (l)

A 
orbital shape
s = 0
p = 1
d = 2
f = 3
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19
Q

Magnetic quantum number (ml)

A

orientations
if l=0, ml=0
if l=1, ml= -1, 0, +1
if l=2, ml= -2, -1, 0, +1, +2

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20
Q

Spin orientation quantum number (ms)

A

spin

ms= +1/2 and -1/2

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21
Q

Electron density map vs nodes

A

Electron density map: probability of finding electrons at a certain distance from the nucleus
Nodes: region where there is zero probability of finding the electron

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22
Q

What is the energy of a photon of green light of wavelength 530nm? What is the energy of a mole of these photons?

A 
Ephoton = ch/landa
Ephoton = 3.7*10^-19 J

(3.710^-19 J)(6.02210^23 mol^-1)
E of a mole of these photons = 230 000 J/mol

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23
Q

The minimum energy needed to remove an electron from a potassium metal surface is 3.710^-19 J. Will photons of frequencies 4.310^14 s^-1 (red light) and of 7.5*10^14 s^-1 (blue light) trigger the photoelectric effect? If so, what is the maximum kinetic energy of the ejected electrons?

A

threshold frequency= 5.6*10^14 s^-1

Ephoton=hv or v=E/h

for red light: 5.610^14 s^-1 (under the threshold frequency, so no electrons will be emitted)
for blue light: 7.510^14 s^-1
5.0*10^-19 J is Ephoton

Ek= Ephoton - Ebinding 
Ek= 1.3*10^-19 J
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24
Q

What is the energy change when the electron in a hydrogen atom changes from the fifth energy state to the second energy state? What is the wavelength of the photon emitted?

A

*emission (negative energy)

En= -2.18*10^-18 (1/nf^2 - 1/ni^2)
    = -4.58*10^-19 J
    = (absolute value) 4.58*10^-19 J
landa= hc/E
         = 4.34*10^-7 m or 434 nm
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25
Q

Compare the wavelengths of an electron travelling at 3.0*10^6 m/s and a ping pong ball of mass 11g travelling at 3.0 m/s.

A

landa= h/mv

electron: 2.410^-10 m
pin pong ball: 210^-32 m

26
Q

What is the wavelength of an electron with 1.310^-19 J of kinetic energy and 7.510^14 s^-1 as its frequency?

A 
Ek= 1/2 mv^2
v= 4.981*10^5 m/s
landa= h/mv
landa= 1.46*10^-9 m
27
Q

Determine how many possible valid sets of quantum numbers exist for a electron in a 5p orbital, and give two examples.

A

5p means n=5 and l=1

possibilities:

n l ml ms
5 1 -1 +1/2
5 1 -1 -1/2
5 1 0 +1/2
5 1 0 -1/2
5 1 1 +1/2
5 1 1 -1/2
28
Q

If the frequency of a light wave were to be increased what would happen to the light waves corresponding wavelength?

a) decrease
b) increase
c) stay the same
d) not enough information is given to answer the question
e) nothing because frequency is related to amplitude

A

a) decrease

E= hc/landa

29
Q

What is the energy in joules of the 337.1 nm spectral line of a nitrogen laser?

a) 1.9710^-25 J
b) 4.5210^-28 J
c) 352 619 J
d) 5.8610^-19 J
e) 4.3510^-31 J

A

d) 5.86*10^-19 J

energy has to be in the *10^-18 and *10^-19 range

30
Q

A student was performing an experiment to demonstrate the photoelectric effect. When the student shone red light from the source on the metal surface, electrons were ejected because:

a) the amplitude of the light was sufficient to cause electron ejection
b) the threshold frequency of the metal surface was less than the frequency of red light
c) the threshold frequency of the metal surface was greater than the frequency of red light
d) the intensity of the light was sufficient to cause electron ejection
e) none of the above is correct

A

b) the threshold frequency of the metal surface was less than the frequency of red light

31
Q

If one wanted to increase the wavelength of an electron ejected from a metal surface during a photoelectric effect experiment which one of the following would be appropriate?

a) find an electron with a smaller mass
b) find an electron with a larger mass
c) increase the wavelength of the photon used to eject the electron
d) decrease the wavelength of the photon used to eject the electron
e) it is not possible to change the wavelength of a free electron

A

c) increase the wavelength of the photon used to eject the electron
landa= h/mv
*frequency is the only thing I can change

32
Q

What is the de Broglie wavelength of an electron with a velocity of 1.00*10^6 m/s?

A

landa= h/mv

= 7.27*10^-10 m or 0.727 nm

33
Q

When sodium metal is bombarded with ultraviolet radiation of wavelength 475 nm, electrons with kinetic energy of 30.0 kj/mol are ejected. What is the binding energy of sodium metal in kj/mol?

A

Ephoton= hc/landa
=4.1810^-19J
Ek of ejected electron =4.9810^-20 J/particle

Ebinding = Ephoton - Ek
= 3.68*10^-19J/particle or 222 kJ/mol

34
Q

Which of the following statements is correct concerning atomic orbitals?

a) an atomic orbital is a region of space where one can precisely determine where an electron can be found
b) an atomic orbital is the region in space occupied by all of the electrons in an atom
c) an atomic orbital is the region in space occupied by electron density in a molecule
d) an atomic orbital can hold at most two electrons
e) an atomic orbital cannot have any radial nodes

A

d) an atomic orbital can hold at most two electrons

35
Q

Electron density

A

where all of the electrons are found

36
Q

A cup of coffee is heated in a microwave overn. 3.0 J of energy is required to raise the temperature of one gram of coffee by on degree Celsius. This energy is provided by microwave radiation having a wavelength of 1.55*10^-2 m. How many photons of microwave radiation must 250 g of coffee absorb to raise its temperature from 20 degrees to 80 degrees Celsius?
How many moles of photons?

A

(3.oJ/1g*degrees celsius) (250g) (60 degrees celsius) =
45 000J

E= hc/landa
= 1.28*10^-23 J/photon

45 000J/ (1.2810^-23 J/photon)
= 3.510^27 photons

=5831 moles

37
Q

Work function

A

minimum amount of energy required to free an electron from the metal surface

38
Q

Uncertainty principle:

the more precisely a particle’s _____ is known, the less precisely that particle’s _______ is known

A

energy

time interval of measurement

39
Q

Ground state vs excited state

A

ground state: lowest energy state of an atom

excited state: when an atom absorbs a photon

40
Q

The first ionization, E, of a carbon atom is 1.81 aJ. What is the wavelength of light , in nm, that is just sufficient to ionize a carbon atom?

A

landa= hc/E

= 1.1010^-7 m or 1.1010^2 nm

41
Q

Consider a sample of excited atoms that lie 3.343*10^-19J above the ground state. Determine the emission wavelength (in nm) of these atoms.

A

landa= hc/E

= 5.942*10^-7 m or 594.2 nm

42
Q

The threshold wavelength for the photoelectric effect for silver is 262 nm. What is the work function for silver? What is the kinetic energy of an emitted electron if the incident light has a wavelength of 227 nm?

A

Work function:
E= hc/ landa
= 7.58*10^-19 J

Kinetic energy:
Ek= Ephoton - Ebinding (in this case work function)
= 8.7510^-19 J - 7.5810^-19 J
= 1.17*10^-19 J

43
Q

Find the threshold frequency needed to eject electrons from a metal with a threshold frequency of 2.40*10^14 s^-1. With what maximum kinetic energy will electrons be ejected when this metal is exposed to light with a wavelength of 245 nm?

A

Threshold frequency:
E=hv
= 1.59*10^-19 J

Maximum kinetic energy:
Ek= Ephoton- Ebinding
= 8.1110^-19 J - 1.5910^-19 J
= 6.52*10^-19 J

44
Q

Calculate the energy of a photon emitted when an electron in a hydrogen atom undergoes a transition from n=6 to n=1.

A

E= -2.17910^-18 J (1/nf^2 - 1/ni^2)
= -2.11810^-18 J
= (absolute value) 2.118*10^-18 J

45
Q

The energy levels of one-electron ions are given by the equation En= (-2.18 aJ)(z^2 / n^2) where Z is the atomic number, n is the energy level, and aJ is the abbreviation for attajoules. Calculate the ionization energy, IE, of the one-electron ion Be3+. The electron starts in the lowest energy level, n=1.

A

IE= 2.18 aJ * Z^2

= 34.88 aJ

46
Q

Assuming that the smallest measurable wavelength in an experiment is 0.710 fm, what is the maximum mass of an object traveling at 885 m*s^-1 for which the de Broglie wavelength is observable?

A

landa= h/mv
m= h/landav
= 1.0510^-21 kg

47
Q

What is the wavelength of the matter wave associated with a proton moving at 1016 m/s?

A

landa= h/mv

= 3.898*10^-10 m

48
Q

What is the wavelength of the matter wave associated with a proton moving at 1016 m/s with a 89 kg astronaut moving at the same speed?

A

landa= h/mv

= 7.3*10^-39 m

49
Q

Write the quantum numbers n and l and select all possible values for ml for each subshell of the element.

a) 3s^2
b) 3p^3

A

a) n=3, l=0, ml=0

b) n=3, l=1, ml= -1, 0, +1

50
Q

For each electron in a ground state Be atom, select the set of quantum numbers that represent it (all that apply).

a) n=1, l=0, ml= 0, ms= -1/2
b) n=2, l=0, ml= 0, ms= -1/2
c) n=1, l=0, ml= 0, ms= +1/2
d) n=1, l=0, ml= -1, ms= +1/2
e) n=2, l=1, ml= 1, ms= +1/2
f) n=2, l=1, ml= 0, ms= -1/2
g) n=2, l=0, ml= 0, ms= -1
h) n=2, l=0, ml= 0, ms= +1/2

A

a) n=1, l=0, ml= 0, ms= -1/2
b) n=2, l=0, ml= 0, ms= -1/2
c) n=1, l=0, ml= 0, ms= +1/2
h) n=2, l=0, ml= 0, ms= +1/2

51
Q

For a hydrogen-like atom, classify these electron transitions by whether they result in the absorption or emission of light.
a) n=1 to n= 3
b) n=2 to n= 1
c) n=3 to n=5
d) n=3 to n=2
Ignoring sign, which transition is associated with the greatest energy change?

A

absorption:

a) n=1 to n= 3
c) n=3 to n=5

emission:

b) n=2 to n= 1
d) n=3 to n=2

greatest energy change:
a) n=1 to n= 3

52
Q

Which subshell is designed by each set of quantum numbers below?

a) n=2, l=0
b) n=4, l=1
c) n=5, l=0
d) n=3, l=1

A

a) 2s
b) 4p
c) 5s
d) 3p

53
Q

Consider a single photon with a wavelength of landa, a frequency of v and an energy of E. What is the wavelength, frequency and energy of a pulse of light containing 100 of these photons?

a) 100 landa, 100v and 100E
b) 0.01 landa, v and 100E
c) landa, v, 100E
d) 100 landa, 100 v, and E
e) 0.01 landa, 0.01v, and 0.01 E

A

c) landa, v, 100E

54
Q

Hydrogen atoms are excited by a laser to the n=4 state and then allowed to emit. What is the maximum number of distinct emission spectral lines that can be observed from this system?

A 
4 to 3
4 to 2
4 to 1
3 to 2
3 to 1
2 to 1

6 total

55
Q

The elements of which group in the periodic table release the most energy by gaining an electron?

A

group 7A

56
Q

The elements of which group in the periodic table absorb the most energy when gaining an electron?

A

group 8A

57
Q

True or False. The higher the value of the l quantum number, the more the orbital is screened by electrons in smaller, more stable orbitals.

A

True.

58
Q

To resolve an object in an electron microscope, the wavelength of the electrons must be close to the diameter of the object. What kinetic energy must the electrons have in order to resolve a protein molecule that is 4.40 nm in diameter?

A

landa= h/mv
v=h/m*landa
= 165000 m/s

Ek= 1/2 mv^2
= 1.24*10^-20 J

59
Q

How many angular nodes does an atomic 6d orbital have?

a) 0
b) 1
c) 2
d) 4
e) 5

A

c) 2

60
Q

How many nodes do the s, p, d and f orbitals each have?

A

s has none
p has 1
d has two
f has three

Chem 1300 (7 decks)

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