Exam 3 Flashcards
Quantum Mechanics and why it was created
the study of anything small
* ex: subatomic, atomic, etc.
Quantum Mechanics was created because before, the equations at the time predicted that light that comes from a BBR that is glowing white would be infinitely intense and that anyone looking at a white light would be incinerated
Also, it was created to understand the structure of an atom
Electromagnetic Radiation
light energy
* Textbook definition: a form of energy transmission in which electric and magnetic fields are propagated as waves through empty space (a vacuum) or through a medium, such as glass
Energy (E)
property that must be transferred to do work
Kinetic Energy
energy in motion
Potential Energy
stored energy
Chemical Energy
energy stored in chemical bonds
Heat Energy (q)
energy due to a temperature change
Rainbow
full spectrum of white light (sunlight)
Speed of light (c)
Formulas:
* c = 𝜈 x λ
* c = 3.00 x 10^8 m/s
Unit:
* m/s
Blackbody Radiator
materials that glow when they get hot
* ex: coal, metals, sun
* produce continuous emission spectras
Photoelectric Effect
- When light strikes the surface of certain metals, electrons are ejected
- the energy of incoming light has to reach a certain threshold frequency before the electrons are ejected
- the number of electrons emitted depends on the intensity of the incident light, but the kinetic energies of the emitted electrons depend on the frequency of the light
- INTENSITY OF LIGHT DOES NOT AFFECT KE
Dual Nature of Light
describes light as a wave made out of particles
* light has particle-like properties (think of photons) and wave-like properties (think about the dispersion of light into a spectrum by a prism)
Photons
particles of light
Planck’s Model
Esingle photon = h x 𝜈
h= 6.63 x 10^-34 Jxs
Equation for kinetic energy flying off metal (photoelectron)
KE = h𝜈 - h𝜈initial
h𝜈 - energy given to the metal from the lamp
h𝜈initial - energy required to eject electron from the metal (threshold energy)
Waves
repetitive disturbances moving through a medium
Wavelength (λ)
distance from crest to crest or trough to trough
Equations:
λ = c / 𝜈
Unit: m or nm
Amplitude
height of the wave
Frequency (𝜈)
the number of waves that pass through a region per second
𝜈 = λ / c
Unit: Hz (1/s)
Wave interference
when two or more waves come in contact
* either constructive interference (creates a bigger wave) or destructive interference (creates a smaller wave)
Constructive Interference
occurs when crests and troughs of a wave line up and they are in sync
* results in a new wave of larger amplitude
* think +
Destructive Interference
occurs when waves are not aligned so the crest of one wave aligns with the trough of another
* results in either a new wave of smaller amplitude or the interacting waves cancel each other out
* think -
Diffraction
patterns that result from wave interference
In the diffraction pattern in water we observed in class…
bright spots meant constructive interference and darker spots represented destructive interference
Standing wave
a wave that bounces back and forth within confinement
* ex: guitar string + think of the slinky experiment
Because standing waves are trapped/confined, they only exhibit a handful of wavelengths and frequencies. This relates to how we can only see certain waves through the spectroscope
Emission
light given off by a material as a result of absorption of light/energy
*different than transmittance
*occurs when enough energy is absorbed by an atom, causing it to give off electrons, which then results in the emission of light
De Broglie’s Wavelength (λd)
λd = h/p
p = momentum = mass x velocity
Unit = m or nm
how we see colors
If you are blue, you are absorbing orange/red light (complementary color) and the blue light passes through
Dual Nature of all Small Particles
De Broglie hypothesized that small particles of matter may at times display wave-like properties
(small = mass of an electron = 9.1 x 10^-31 kg)
Dilution
adding solvent to increase the volume and lower the concentration of a sample
equation: c1 x v1 = c2 x v2
Uncertainty of Wave Principle
when there are multiple waves…
* the location of the wave cannot be defined but the wavelength can be defined
when there is a single wave…
* the location of the wave can be defined but the wavelength can’t
THE MORE WE KNOW ABOUT LOCATION, THE LESS WE KNOW THE LENGTH OF THE WAVE
* Summarized by Heisenberg’s Uncertainty Principle
σx*σp ≥ h / 4π
* σx = uncertainty in location
* σp = uncertainty in momentum
Bohr’s Model of the Atom
planetary model
* dense nucleus with neutrons and protons and electrons revolve around it like planets
* each orbit has a number (“n”) with the smallest orbit, closest to the nucleus n=1 n will always be a constant
* n 1 is the ground state and anything above it is an excited state.
* An atom emits energy as a photon when the electron falls from an orbit of higher energy and larger radius to an orbit of lower energy and smaller radius
* The radius of an orbit depends on the n #
rn = n^2 x a0
* a0 = Bohr’s radius 0. 53 x 10^−10m
relationship of n and energy
electrons pass from one n-level to another using fixed amounts of E
low n-levels -> high n-levels = gain (absorb) energy
high n-levels -> low n-levels = lose (emit) energy
* En = -Rh/n^2
* △E = -Rh( 1/n^2f - 1/n^2i )
* * positive = absorbance and negative = emission
Emission
Emission occurs when enough energy is absorbed by an atom, causing it to give off electrons, which then results in the emission of light.
* peaks pointing down on the substance’s atomic emission spectra graph
* you add energy to a substance like the elements in the discharge tube and they get excited and start to emit light.
* electron comes down n-levels
Transmittance (T)
the amount of light that passes through a solution without being absorbed
Absorbance (A)
the amount of energy/light taken in by particles in a solution
* has an inverse relationship with transmittance
* peaks pointing up on the substance’s atomic emission spectra graph
*the electron goes up an n-level
Threshold frequency (Ф)
the minimum energy/frequency required by incoming light in order to eject or release electrons from the surface of a metal
When an electron transitions to a higher n-level it (releases/gains)
Gains because they need more energy to go up in levels like you would need energy to climb up a ladder
When an electron transitions to a lower n-level it (releases/gains) energy
releases, emission
If something is glowing it is…
- emitting light
- an upwards peak on the substance’s emission spectra
Interpreting Emission Spectra graphs
Where there are dips in the graph represent to where you
λmax
the wavelength where the compound absorbs the maximum amount of light (photons)
* at this wavelength, a slight change in concentration allows for a significant change in the absorbance
* used for Beer’s law
continuous vs discrete emission spectra
Black body radiators like the sun and coal have continuous emission spectrums (all of the colors/wavelengths present through spectrometer) while things like elements have discrete emission spectra (quantifiable).
This is because BBRs like sunlight and incandescent light have more different types of molecules/elements interacting w/ the light. Since the discharge tubes were concentrated with specific elements, the wavelengths that are transmitted are at specific points, representing the change in energy as electrons get as they change n-levels.
How we see color
Things absorb wavelengths that correspond to their complementary color and transmit wavelengths (let pass through) of the color that they are
* ex: Red dye absorbs blue/green wavelengths and red wavelengths pass through
Dye experiment vs discharge tube experiment
In Lab 5, the sharpness of the peaks was because the electrons of ATOMS are very specifically localized to energy levels, and their jumps between energy levels require specific energy changes
In lab 6 (food dyes), the peaks were broad because others are a lot of electrons in a MOLECULE and they’re all jumping around different MOLECULAR energy levels.
Relationship between absorbance, concentration, and path length
When concentration increases, absorbance increases because there are more molecules present to interact with the light. As path length increases, absorbance increases because there are more molecules present and concentration also increases.
* ONLY FOR LOW CONCENTRATIONS AND ABSORBANCES BELOW 1
* at high concentrations, the molecules are no longer independent of one another
gaps between energy levels
larger gaps between energy levels require shorter wavelengths of light (higher frequency and higher energy) for an electron to make that jump
-purple light - short wavelength, high frequency, high energy
the energy of the electrons depends on the molecular structure
alternating single and double bonds make it so that electrons are shared across multiple bonds (delocalization)
*longer molecules have smaller energy gaps (changes in energy) between their energy levels and vice versa
