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Chem 135 Test 1 > Quantum Theory and Atomic Structure > Flashcards

Quantum Theory and Atomic Structure Flashcards

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1
Q

What are the wave properties of electromagnetic radiation?

A

Frequency and Wavelength

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2
Q

How does electromagnetic radiation travel?

A

Electromagnetic radiation
travels as waves—the
result of oscillating
electric and magnetic
fields moving
simultaneously through
space

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3
Q

Define Frequency.

A

Frequency (n) is
the number of cycles the
wave makes per second,
expressed in units of
1/second (s –1 ), or
hertz (Hz)

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4
Q

Define wavelength.

A

(λ) is the distance between any point
on a wave and the corresponding point on the next wave. Expressed in in meters, nanometers, picometers and angstroms.

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5
Q

Define speed of wave.

A

(m/s) is the product of its frequency (cycles
per second) and its wavelength (meters per cycle).

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6
Q

Define the speed of light and what number it travels at.

A

Speed of light is a fundamental physical constant that is the speed at which electromagnetic radiation travels in a vacuum. It travels at 3.00 x 10^8 m/s.

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7
Q

Frequency Practice Problem: A dentist uses x-rays (l=1.00 Å) while a patient listens to
an FM radio station ( λ=325 cm) and looks out the window at blue
sky ( λ=473 nm). What is the frequency ( s –1 ) of the EM from each?

A
  • Add picture here
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8
Q

What is the difference between diffraction and refraction?

A

Defraction: Bending of waves around obstacles and openings. It increases with increasing wavelengths.

Refraction is the change of direction of waves that occurs when waves travels from one medium to another, accompanied by wavelength and speed change.

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9
Q

What is a condition for a diffraction pattern?

A

If light waves pass
through two adjacent
slits, the emerging
circular waves
interact through
interference

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10
Q

What is the difference between crests of waves and beam of particles pattern?

A

Crests of waves: If a wave passes through a slit about as wide as its wavelength, it forms a semi-circular wave on the other side of the opening.

Beam of particles: Some particles hit the edge and stop; going through a linearly narrower stream

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11
Q

Define blackbody radiation.

A

Describes the relationship between an object’s temperature, and the wavelength of electromagnetic radiation it emits.

A black body is an idealized object that absorbs all electromagnetic radiation it comes in contact with.

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12
Q

What happens to an object when it is heated? (What colours in what order…)

A

When an object is heated, it begins to emit visible light, first as a red glow, then orange and then white light.

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13
Q

Blackbody radiation attemps to use ______________ to predict wavelengths of the emitted light _______.

A

Electromagnetic theory, Failed.

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14
Q

What did Max Planck propose?

A

He proposed that the hot, glowing object could emit
(or absorb) only certain amounts of energy: E = nhv

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15
Q

What does each letter represent in E: nhv?

A
  • E is the radiation energy
  • v is its frequency,
  • n is a positive
    integer called a quantum number
  • h is Planck’s constant
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16
Q

What constant is h?

A

Measured in units of Jxs, h= 6.626 x 10^-34 Jxs

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17
Q

Define a quantum.

A

Each change in energy results from a “packet” of energy being gained or lost by the atom. Aka energy packet

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18
Q

Is energy of an atom continuous or quantized? Explain why.

A

Quantized - it can exist only in certain fixed amounts.

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19
Q

If atoms can emit only fixed amounts of energy, it follows that atoms can have only _____________________: E = 1hv, 2hv,…

A

Fixed electronic energy values

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20
Q

An atom changes its ______ state by _______ or ________ a quantum of energy.

A

energy, emitting, absorbing

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21
Q

What is the formula for an atom changing its energy state by emitting or absorbing a quantum of energy?

A

△Eatom: Eemitted (or absorbed) radiation: △nhv

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22
Q

What is the photoelectric effect?

A

When monochromatic light of sufficient energy hits the metal plate, an electric current flows

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23
Q

What are the two conditions for the photoelectric effect that Einstein offered?

A
  1. Presence of a threshold frequency. Light shining on the metal must have a minimum frequency (which varies with the metal), or no current flows.
  2. Absence of a time lag. Current flows the moment that light of high enough
    frequency shines on the metal, regardless of its intensity.
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24
Q

What theory did Albert Einstein propose to help explain the photoelectric effect?

A

Photon theory - he proposed that radiation is particulate, occurring as quanta of
electromagnetic energy, later called photons.

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25
Q

What is the equation for the energy of a photon?

A

Ephoton: hv : △Eatom

An atom changes its energy when it absorbs/emits a photon, a “piece” of light whose energy is fixed by its frequency

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26
Q

Photon Practice problem: A microwave oven has a frequency of 2.45 x 10^9 s –1. What is the energy of one photon of this microwave radiation?

A

E: hv : (6.626 x 10^-34 Jxs)(2.45 x 10^9 s-1) : 1.62 x 10^-24 J

27
Q

How did Albert’s theory explain the presence of a threshold frequency in the photoelectric effect?

A
  • A beam of light is composed of enormous numbers of photons.
  • An electron is freed only when one photon of a certain minimum
    energy is absorbed. Energy depends on frequency (hxv), so a threshold frequency is to be expected.
28
Q

How did Albert’s theory explain the absence of a time lag in the photoelectric effect?

A
  • Current will be less in dim light than in bright light since fewer photons with enough energy eject fewer electrons per unit time
29
Q

What happens when an element is vaporized?

A

Otherwise known as thermally or electrically excited, it emits light.

Produces a line spectrum, a series of fine lines of individual colours.

30
Q

What colour does hydrogen gas give?

A

A pinkish color

31
Q

Spectroscopists discovered several series of H spectral lines in other regions of the electromagnetic spectrum. How does this pattern look?

A
  • Add picture here
32
Q

What is the Rydberg equation and what does it predict?

A

Predicts the position and wavelength of any line in a given series

  • Add equation picture here
33
Q

Is the Rydberg equation empirical or molecular?

A

Empirical

34
Q

What is the Bohr model of the hydrogen atom?

A

Bohr proposed that atoms do not radiate energy while in one of their fixed stationary energy states

35
Q

What happens to an electron when it moves to a different orbit?

A

The atom changes to another energy state. This happens only by the atom absorbing or emitting a photon.

36
Q

What does the photon energy equal?

A

Equals the difference in energy between the two stationary states:

Ephoton: △Estationary states: hv

37
Q

Spectral lines represent ________ of a photon of specific energy as an electron ______ from a higher energy state to a lower one

A

emission, drops

38
Q

Why does the atomic spectrum consists of lines instead of a continuum?

A

Because the atom’s energy has only certain discrete levels or states

39
Q

In Bohr’s model, what does the quantum n represent and how is it related to the atom’s energy?

A

Determines the radius of
the electron’s orbit, directly related to the atom’s energy.

The lower the value of n, the smaller is the radius of the orbit and the lower is the energy level of the atom.

40
Q

Which energy level is the ground state and which are the excited state?

A

When the electron is in the n = 1 orbit, the atom is in its lowest (first) energy level, called the ground state.

The second energy level (second stationary state) and all higher levels are called excited states.

41
Q

How can a hydrogen atom in the 2nd energy level return to the ground state?

A

By emitting a photon of a particular frequency

Ephoton: hv: Efirst excited state - Eground state

42
Q

When a sample of atomic hydrogen absorbs energy, do different hydrogen atoms absorb different or the same amounts?

A

Different

43
Q

When does infrared, visible and ultraviolet series happen? In which transitions?

A

Transitions from outer orbits to n = 3 gives the infrared series of spectral lines.

Transitions from outer orbits to n = 2 gives the visible series of spectral lines.

Transitions from outer orbits to n = 1 gives the ultraviolet series of lines.

44
Q

Define zero energy.

A

(E = 0) as the state when the electron is totally removed from the nucleus; in other words, when n = ∞

E<0 (negative) for any smaller n values

45
Q

The energy difference between any two energy levels is given by:

A
  • Add picture here
46
Q

How much energy is needed to completely remove the electron from the hydrogen atom? Is it positive or negative and why?

A

2.18 x 10^-18 J

Positive because energy must be absorbed to remove the electron from the positive nucleus.

47
Q

What is ionization energy and what is it of the hydrogen atom?

A

Ionization: the amount of energy required to remove an electron from an isolated atom or molecule.

1.31 x 10^3 kj/mol

48
Q

Does the Bohr model work for all elements?

A

No, The model worked well for one-electron species, but not for atoms or ions with more than one electron.

49
Q

How is an object’s mass and wavelength related?

A

An object’s wavelength is inversely proportional to its mass; heavy objects have wavelengths that are very much smaller than the object

50
Q

How many wavelengths do fast moving electrons have?

A

Close to the size of an
atom (~10^–10 m).

51
Q

If electrons were wavelike and restricted to orbits of fixed radii, only certain possible ________ and ________ would be allowed.

A

frequencies, energies

52
Q

what was broglie’s theory?

A

he said atoms are like other systems that display only certain allowed states and suggested that particles of matter such as electrons have some properties of waves.

if de Broglie’s concept is correct, electrons should exhibit the wave properties of diffraction and interference.

53
Q

what is the uncertainty principle?

A

it is impossible to know simultaneously the exact position and velocity of a particle like an electron.

54
Q

How can we find the probability of finding an electron in a given volume of space?

A

Each Ψ describes a fixed-energy state the electron can occupy and Ψ2 gives the probability of finding it in a given 3-dimensional space

55
Q

what does Ψ and Ψ2 represent?

A

Ψ : atomic orbital
Ψ2: probability of the electron being at a distance r from the nucleus

56
Q

electron probability density in the H atom _____ state

A

ground

57
Q

where does the electron spend 90% of its time?

A

ground state

at the same distance that the bohr model predicted it to spent all of its time

58
Q

what is the maximum radial probability for the ground state of H atom?

A

5.29 x 10^-10 m

59
Q

what are the energy levels of the hydrogen atom?

A
  • in the ground state, the electron is in the n = 1 shell (1s orbital)
  • photons of the correct energies can promote the electron to higher shells
  • the excited atom can return to the ground state by emitting a photon of the same energy
60
Q

what does n, l and ml mean?

A

n: relative size of orbital and eneergy level of H atom. the higher the n value, the greater the energy.

l: shape of the orbital. the number of possible l values equals the value of n.

ml: orientation of the orbital in the 3d space of nucleus. orbital with l: 0 can have ml: 0. orbital with l:1 can have ml: -1,0 or +1.

61
Q

Each subshell is designated by a letter. What does l:0,1,2,3 mean?

A

l:0 –> s subshell
l:1 –> p subshell
l:2 –> d subshell
l:3 –> f subshell

62
Q

what are the shapes of the s node orbital?

A

spherically symmetrical around the nucleus

63
Q

what are the shapes of the p node orbital?

A

has two regions of higher probability that lie on either side of the nucleus.

mutually perpendicular p orbitals, equivalent in size, shape and energy, differing only in orientation

64
Q

what are the shapes of the d node orbital?

A

5 different orientations

the 4d orbitals extend farther from the nucleus than the 3d, and the 5d orbitals extend still farther

Chem 135 Test 1 (2 decks)

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