Chapter 12 - Quantum Mechanics and Atomic Theory

Question 1

Describe electromagnetic radiation and its properties

Answer 1

• has electrical and magnetic
  fields that simultaneously oscillate in planes mutually perpendicular to
  each other and to the direction of propagation through space
• characterized by wavelength (lambda), frequency (v), speed
• wavelength = distance between two consecutive peaks or troughs in a wave.
• frequency: number of waves (cycles)
  per second that pass a given point in space
• can be seen as stream of particles called photons, each with energy hv (h is Planck’s constant)

Question 2

Explain the photoelectric effect

Answer 2

• When light strikes a metal surface, electrons are emitted
• Analysis of the kinetic energy and numbers of the emitted electrons led Einstein to suggest that electromagnetic radiation can be viewed as a
  stream of photons

Question 3

Explain the Hydrogen spectrum

Answer 3

• The emission spectrum of hydrogen shows discrete wavelengths
• Indicates that hydrogen has discrete energy levels

Question 4

Explain the Bohr model of the hydrogen atom

Answer 4

• Using the data from the hydrogen spectrum and assuming angular momentum
  to be quantized, Bohr devised a model in which the electron traveled in circular orbits
• Although an important pioneering effort, this model proved to be entirely
  incorrect

Question 5

Explain the wave/quantum mechanical model and the Heisenberg uncertainty principle

Answer 5

• An electron is described as a standing wave
• The square of the wave function (often called an orbital) gives a probability distribution for the electron position
• The exact position of the electron is never known, which is consistent with the Heisenberg uncertainty principle: it is impossible to know accurately
  both the position and the momentum of a particle simultaneously
• Probability maps are used to define orbital shapes
• Orbitals are characterized by the quantum numbers n, l, and ml

Question 6

Describe electron spin and the Pauli exclusion principle

Answer 6

Described by the spin quantum number ms, which can have values of +/- 1/2

• Pauli exclusion principle: no two electrons in a given atom can have the same set of quantum numbers
• Only two electrons with opposite spins can occupy a given orbital

Question 7

Explain what it means for energy to be quantized

Answer 7

Energy can only be lost or gained in certain amounts (photons); integer multiples of hv.

Question 8

Explain interference of waves

Answer 8

constructive = in phase, light gets brighter 
destructive = out of phase, light gets darker

Question 9

Describe the wave function.

Answer 9

wave function, in quantum mechanics, variable quantity that mathematically describes the wave characteristics of a particle. The value of the wave function of a particle at a given point of space and time is related to the likelihood of the particle’s being there at the time.
The square of the function evaluated
at a particular point in space indicates the probability of finding an electron near that point.

Question 10

Explain the quantum numbers and their possible values, as well as how to determine nodes.

Answer 10

Principle quantum number - n = 1 - infinity
Angular momentum quantum number - l = 0 to (n-1)
Magnetic quantum number - ml = -l to +l
Electron spin - ms = +/- 1/2
l is equal to number of angular nodes
radial nodes = n-l-1
total nodes = n-1

Question 11

Explain the Aufbau principle

Answer 11

As protons are added one by one to the nucleus to build up the elements, electrons
are similarly added to these atomic orbitals.

Question 12

Explain periodic trends related to IE, EA, radii,

Answer 12

IE and EA increases across period, decreases down a group

Radii increase down a group and decreases across a period