Color?
Hi,
My textbook says, "The only photons absorbed are those whose energy is exactly equal to the energy difference between the ground state and an excited state, and this energy difference varies from one kind of molecule to another.” Why does it vary from one kind of molecule to another?
Also, we see color because that specific wavelength has been reflected, or has been transmitted, to our eyes. What happens in reflection? Do the electrons totally reject the incoming photon and send it back to us?
And with absorption, why is it that sometimes heat is given off and not light, and sometimes light is given off? When objects absorb wavelengths, don’t the colors just disappear from our sight? Why and when, according to the thing about electrons being excited and falling back to ground state, are photons reemitted?
Along the similar vein, what happens during the transmission of specific wavelengths?
Thanks.
My textbook says, "The only photons absorbed are those whose energy is exactly equal to the energy difference between the ground state and an excited state, and this energy difference varies from one kind of molecule to another.” Why does it vary from one kind of molecule to another?
Also, we see color because that specific wavelength has been reflected, or has been transmitted, to our eyes. What happens in reflection? Do the electrons totally reject the incoming photon and send it back to us?
And with absorption, why is it that sometimes heat is given off and not light, and sometimes light is given off? When objects absorb wavelengths, don’t the colors just disappear from our sight? Why and when, according to the thing about electrons being excited and falling back to ground state, are photons reemitted?
Along the similar vein, what happens during the transmission of specific wavelengths?
Thanks.
(edited 9 years ago)
I see. Thanks.
Anybody help me answer the rest?
Anybody help me answer the rest?
The previous answer really isn't a very good one.
Your question has a very complicated answer.
In molecules, electrons inhabit different molecular energy levels. When exposed to some form of radiation, the electrons can change their energy level.
Now, a quantum mechanical rule says that an electron can only change its energy if it receives an amount of energy from a photon of exactly the correct energy to account for the difference between its current energy level, and the excited state energy level.
Now, because a photon is a quanta of electromagnetic radiation, its energy and its frequency are proportional (by Planck's constant). Hence, only photons of EMR of particular wavelengths can affect particular molecular excitations. Now, different molecules have different molecular energy levels, changing anything about the molecule's structure will change these levels accordingly.
When we see colour, we are detecting photons of the correct frequency to be identified as, say, blue. Take for example a pair of jeans.
The dye in the jeans will absorb a mixture of photons corresponding to the energy transition gap between the highest occupied molecular energy level and the lowest unoccupied molecular energy level. Because they look blue, we know that there is no energy gap whose energy is equal to the frequency of blue light multiplied by Plank's constant. As the photon is not absorbed by the jeans, then it is just reflected. So yes, it is "rejected", after a fashion. It simply doesn't interact with the electrons.
"Heat" is a part of the electromagnetic spectrum, remember. -Infrared.
Your question has a very complicated answer.
In molecules, electrons inhabit different molecular energy levels. When exposed to some form of radiation, the electrons can change their energy level.
Now, a quantum mechanical rule says that an electron can only change its energy if it receives an amount of energy from a photon of exactly the correct energy to account for the difference between its current energy level, and the excited state energy level.
Now, because a photon is a quanta of electromagnetic radiation, its energy and its frequency are proportional (by Planck's constant). Hence, only photons of EMR of particular wavelengths can affect particular molecular excitations. Now, different molecules have different molecular energy levels, changing anything about the molecule's structure will change these levels accordingly.
When we see colour, we are detecting photons of the correct frequency to be identified as, say, blue. Take for example a pair of jeans.
The dye in the jeans will absorb a mixture of photons corresponding to the energy transition gap between the highest occupied molecular energy level and the lowest unoccupied molecular energy level. Because they look blue, we know that there is no energy gap whose energy is equal to the frequency of blue light multiplied by Plank's constant. As the photon is not absorbed by the jeans, then it is just reflected. So yes, it is "rejected", after a fashion. It simply doesn't interact with the electrons.
"Heat" is a part of the electromagnetic spectrum, remember. -Infrared.
Original post by Infraspecies
The previous answer really isn't a very good one.
Your question has a very complicated answer.
In molecules, electrons inhabit different molecular energy levels. When exposed to some form of radiation, the electrons can change their energy level.
Now, a quantum mechanical rule says that an electron can only change its energy if it receives an amount of energy from a photon of exactly the correct energy to account for the difference between its current energy level, and the excited state energy level.
Now, because a photon is a quanta of electromagnetic radiation, its energy and its frequency are proportional (by Planck's constant). Hence, only photons of EMR of particular wavelengths can affect particular molecular excitations. Now, different molecules have different molecular energy levels, changing anything about the molecule's structure will change these levels accordingly.
When we see colour, we are detecting photons of the correct frequency to be identified as, say, blue. Take for example a pair of jeans.
The dye in the jeans will absorb a mixture of photons corresponding to the energy transition gap between the highest occupied molecular energy level and the lowest unoccupied molecular energy level. Because they look blue, we know that there is no energy gap whose energy is equal to the frequency of blue light multiplied by Plank's constant. As the photon is not absorbed by the jeans, then it is just reflected. So yes, it is "rejected", after a fashion. It simply doesn't interact with the electrons.
"Heat" is a part of the electromagnetic spectrum, remember. -Infrared.
Your question has a very complicated answer.
In molecules, electrons inhabit different molecular energy levels. When exposed to some form of radiation, the electrons can change their energy level.
Now, a quantum mechanical rule says that an electron can only change its energy if it receives an amount of energy from a photon of exactly the correct energy to account for the difference between its current energy level, and the excited state energy level.
Now, because a photon is a quanta of electromagnetic radiation, its energy and its frequency are proportional (by Planck's constant). Hence, only photons of EMR of particular wavelengths can affect particular molecular excitations. Now, different molecules have different molecular energy levels, changing anything about the molecule's structure will change these levels accordingly.
When we see colour, we are detecting photons of the correct frequency to be identified as, say, blue. Take for example a pair of jeans.
The dye in the jeans will absorb a mixture of photons corresponding to the energy transition gap between the highest occupied molecular energy level and the lowest unoccupied molecular energy level. Because they look blue, we know that there is no energy gap whose energy is equal to the frequency of blue light multiplied by Plank's constant. As the photon is not absorbed by the jeans, then it is just reflected. So yes, it is "rejected", after a fashion. It simply doesn't interact with the electrons.
"Heat" is a part of the electromagnetic spectrum, remember. -Infrared.
But why are these photons sometimes transmitted and sometimes reflected? (transparent vs. opaque). And also, I’m still confused about absorption, because once the photon has been absorbed, shouldn’t the energy be released again? Would we not detect that as color?
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