2.5 - Energy Levels & Photo Emission Flashcards
What is ionisation?
The removal, or addition, of an electron from, or to, an atom when given sufficient energy.
What is excitation?
When an electron is given enough energy to move up an energy level, but not enough to leave the atom.
When does florescence occur?
When an electron (in atomic orbit of a mercury atom) is excited and then de-excites, releasing a UV photon.
This UV light excites the electrons in the phosphor coating which, as a result creates a fluorescent glow.
What are photons?
Massless ‘packets’ of electromagnetic energy.
What is the equation to find the energy of a photon?
E = hf
E = hc/λ
h = Plank’s constant
c = speed of light
λ = wavelength
f = frequency
How do you calculate the number of photons incident on a surface per second?
Power of light source / Energy of one photon
What are electron energy levels?
Electrons in an atom can only have a specific amounts of energy. (energy levels are the shells around the atom)
What is the lowest energy level called?
Ground state.
What are 3 ways that electrons gain energy and move up energy levels?
- Collisions with other atoms or electrons
- Absorbing a photon
- A physical source, like heat
What is line spectra?
The wavelengths of light emitted from an element when its electrons de-excite.
What are the 2 types of line spectra?
Emission spectra and absorption spectra.
How do you get a line spectrum?
Passing light from a fluorescent tube through a diffraction grating or prism, you get a line spectrum. Each line in the spectrum represents a different wavelength of light.
What is the emission spectra?
- When a photon is emitted after de-excitation, each transition lets out a different wavelength of light.
- The resulting emission spectrum contains a set of discrete wavelengths, represented by coloured lines on a black background.
What is the absorption spectra?
- When electrons excite after the absorption of a photon. When white light passes through a cool, low pressure gas it is found that light of certain wavelengths are missing, this shows on the spectrum.
- Colour background and black lines (black lines - energy levels)
What can be used as evidence for the discrete energy levels in atoms?
Emission and absorption spectra.
What is the definition of discrete energy levels?
The specific energy levels of emitted photons when electrons in orbit get excited.
What is the equation for energy of the emitted photons in atoms?
ΔE = hf = E₁ - E₂
E₁ = Energy of higher level
E₂ = Energy of the lower level
h = Planck’s constant
f = Frequency of photon (Hz)
Using the wave equation, how do you find the wavelength of the emitted / absorbed radiation?
λ = hc / E₂ - E₁
What is wave-particle duality?
The fact that light behaves as both a particle and a wave.
What is the evidence for wave-particle duality?
- Proof that light behaves like a particle - The photoelectric effect (as light here interacts with matter)
- Proof that light behaves like a wave - The Young’s Double Slit experiment (as light diffracts).
What is the equation to find the De Broglie wavelength?
λ = h /mv
h = Plank’s constant
mv = momentum
What is proof that electrons have wave-like properties?
Electron diffraction as only waves can diffract.
What is the interference pattern of an electron?
Concentric rings.
When are diffraction patters on accelerated electrons observed?
When accelerated electrons in a vacuum tube interact with the space in a graphite crystal.
When does diffraction occur with particles?
When a particle interacts with an object of about the same size as its de Broglie wavelength.
In electron diffraction experiments, what does a smaller accelerating voltage achieve?
Slower electrons, giving more widely-spaced rings.
How can momentum and KE be related? (equations)
E = p²/2m
or
p = √2mE
(E = KE)
How can momentum and KE be used in the de Broglie equation?
λ = h/√2mE
(E = KE)
How is the radius of the diffraction pattern and the wavelength related?
The longer the wavelength, the more the light spreads out, therefore there is a larger radius produced.
(directly proportional)
