3.5 - energy levels and spectra
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72 Terms
what is a rainbow?
a natural display of the colours of the spectrum of sunlight
how can we split white light into a continuous spectrum?
using white light from a filament and a prism
why do rainbows form during rain?
raindrops split the sunlight into a continuous spectrum of colours, therefore forming a visible rainbow
why do we?
great question!
why do we use white light when trying to split light into a continuous spectrum?
because white light is formed by combining the wavelengths of all the colours in the visible light spectrum
why do we use a filament lamp when trying to split light into a continuous spectrum?
idk ask. usually so it’s monochromatic so u polarise it but idk in this case cuz it’s white light so it already isn’t monochromatic
what do we call the array of colours formed by splitting white light?
the continuous spectrum (of colours)
what determines the colour of visible light?
wavelength
what does a prism do?
split white light into a continuous spectrum
what is the wavelength of deep violet light?
< 400nm
what is the wavelength of deep red light?
~ 650nm
what is the wavelength range in the continuous spectrum?
from deep violet (>400nm) to deep red (~650nm)
does the wavelength of visible light in the continuous spectrum increase or decrease?
it increases across the spectrum from deep violet (>400nm) to deep red (~650nm)
which has a shorter wavelength - deep violet or deep red?
deep violet, with a wavelength of >400nm
which has a longer wavelength - deep violet or deep red?
deep red, with a wavelength of ~650nm
what is the wavelength of the light photons in the visible spectrum measured in?
nm (nanometres, x 10-6)
visible light spectrum when light source is;
tube of glowing gas
filament lamp
tube of glowing gas - line spectrum
filament lamp - continuous spectrum
PICTURE
visible light spectrum when light source is a tube of glowing gas
line spectrum
PICTURE HERE
visible light spectrum when light source is a filament lamp
continuous spectrum of colour
PICTURE
which light source produces a line visible light spectrum?
gas from a glowing tube
which light source produces a continuous visible light spectrum?
filament lamp
why does light from a filament lamp produce a continuous visible light spectrum when split?
ASK
why does light from a tube of glowing gas produce a line visible light spectrum when split?
ASK
what does the wavelength of the lines of a line spectrum depend on?
the atoms of the element producing the line spectrum
how do you refer to the light’s composition?
as being composed of light photons with a specific energy level and wavelength characteristic to the atoms of the element
how we identify the element that produces a line spectrum?
by measuring the wavelengths of the lines
why does measuring the wavelength of lines in a line spectrum help identify the element that produced the line spectrum?
because the wavelength of lines produced is characteristic to the element that produces the line spectrum
can elements produce the same pattern of light wavelengths?
no - it’s always individual to the element
what is individual to an element?
the energy levels of the atom
therefore, the photons emitted by atom
therefore, the wavelengths of lines in a line spectrum
therefore, pattern of light wavelengths
why do elements produce an individual pattern of light wavelengths?
the energy levels of an atom, and therefore the photons emitted, is characteristic to each element. this means the wavelength of the photons are also characteristic, so the atoms of each element produce an individual pattern of light wavelengths
why are the photons emitted by an atom characteristic to the element?
because the energy levels are characteristic for the atoms of the element
what is each line in a line spectrum due to?
light of a certain colour, therefore a certain wavelength composing the incident white light
for a single line, do the light photons producing it have the same or different amount of energy?
light photons producing a single line all have the same energy, which is different from the energy of the photons producing other lines
for different lines composing a line spectrum, do the light photons producing them have the same energy as each other?
light photons producing different lines have different amounts of energy
energy levels of photons producing lines in a line spectrum;
photons producing the same line
photons producing different lines to each other
photons producing the same line - same energy as each other
photons producing different lines to each other - different energy as each other
wavelength of photons producing lines in a line spectrum;
photons producing the same line
photons producing different lines to each other
photons producing the same line - same wavelength as each other
photons producing different lines to each other - different wavelengths as each other
why are the photons producing lines in a line spectrum emitted?
when an atom de-excites due to one of its electrons moving to an inner shell
what happens when an atom in a tube of glowing gas de-excites?
it emits a photon with an energy and wavelength that characteristic to the atom its emitted from. this photon goes on to produce a line in a line spectrum
what is the energy of the emitted photons that produce the lines in a line spectrum?
energy of emitted photon (hf) = E1 - E2
h = planck’s constant, 6.63 × 10-34
f = frequency of photon
E1 = energy of higher energy level shell (that the electron de-excites from)
E2 = energy of lower energy level shell (that the electron de-excites to)
energy of emitted photon (hf) = ?
energy of emitted photon (hf) = E1 - E2
h = planck’s constant, 6.63 × 10-34
f = frequency of photon
E1 = energy of higher energy level shell (that the electron de-excites from)
E2 = energy of lower energy level shell (that the electron de-excites to)
what is E2 (shell of lower energy level) if the electron is de-exciting to ground state?
0
why is the energy level of a photon producing a line in a line spectrum hf = E1 - E2?
because the photons producing the lines are photons that have been emitted during de-excitation, therefore the energy level is the de-excitation energy IS THAT THE RIGHT TERM
how can we calculate the frequency of a photon producing a line in a line spectrum?
f = c / λ
f = photon frequency
c = speed of light in a vacuum, 3.0 × 108 ms-1
λ = photon wavelength (wavelength of line on line spectra)
when given an energy level diagram for the atom, how do you calculate the excitation energies?
measure photon wavelength (i.e., wavelength of line in line specta)
f = c / λ to find photon frequency
hf = E1 - E2 to find the missing excitation energy, E2 being 0 if the electron de-excites to ground state
refer to energy level diagram to note the transition that causes a photon of that wavelength to be emitted
what is the simplest type of atom?
hydrogen - with 1 proton, no neutrons, and 1 electron
what is the general formula for the energy levels of a hydrogen atom, relative to the ionisation level?
HERE
what is the general formula for the energy level of a hydrogen atom relative to?
the ionisation level
what is the general equation for the energy of an emitted photon when a hydrogen atom de-excites from energy level n1 to a lower energy level n2?
HERE
electron transition in the hydrogen atom
DIAGRAM HERE
explain this EQUATION OF HYDORGEN PHOTON EMISISON ENERGY LEVEL EQUATION
EXPLANATION HERE EQUATION DERIVATION
each energy level (1 / n1², 1 / n2², etc) corresponds to the energy level of the electron in that particular shell
so the formula gives the energy of a photon released when an electron in the hydrogen atom moves from one shell to a shell at a lower energy
how was the energy level formula for hydrogen deduced?
first deduced from the measurements of the wavelengths of the lines
later, quantum theory was applied to the motion of the electron, producing the first theoretical explanation of the energy level formula
which transition between energy levels in an excited hydrogen atom IS IT JUST HYDROGEN gives the highest energy of the released photon? why?
between n1 and n2 GET THIS EXPLAINED
DIAGRAM OF THE ELECTORN TRANSITION
what are the lines in a spectrum due to?
energy levels, as the energy level determines the wavelength of the photon and therefore the wavelength pattern
what are some real world applications of the measurements of wavelengths of light?
branches in science such as;
astronomy
forensic science
why is the measurement of wavelengths of light important in branches of science?
they help identify the chemical elements in the light source
what can measuring the wavelength of light help identify?
the chemical elements in a light source, i.e., what type of element it is
how was helium discovered?
from the spectrum of sunlight, as a pattern of lines in the spectrum was observed at wavelengths that scientists could not attribute to any known gas, and was therefore the wavelength of a previously unknown element in the sun
how is helium produced?
through the nuclear fusion of hydrogen nuclei in the sun
on earth, produced as alpha particles from the radioactive decay of elements such as uranium
what is the effect of nuclear fusion in the sun?
the production of helium atoms
how is helium produced on earth?
produced as alpha particles from the radioactive decay of elements such as uranium
what is produced through the radioactive decay of elements such as uranium?
helium atoms (alpha particles)
what are the practical uses of helium?
fusion reactions
helium-neon lasers
for temperatures of a very-low temperature
where can helium be stored?
oil wells
at what temperature does helium become a liquid / superfluid?
< 2.17 K, near absolute zero
what is a superfluid?
a fluid with no viscosity, meaning it has ‘no resistance to flow’, i.e., flows without loss of Ek
what is significant about helium in liquid state?
it is a superfluid
what happens to helium at a temperature < 2.17 K?
it becomes a liquid, and therefore a superfluid
what are superfluids resistant to?
flow
what is the viscosity of a superfluid?
0
what is the only noted superfluid?
helium in liquid state
as a superfluid, what is helium in a liquid state able to do?
escape, as a thin film, a container by ‘crawling’ up and over the walls
what form does helium in liquid state take when escaping containers?
a thin film
Note 
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