Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    9
    ReputationRep:
    Each corresponding flame colour is due to the excited electrons falling back to their ground state and releasing a form of energy - namely visible light. Now, according to many websites the higher the energy gap (which increases down Group 2) the higher the frequency of visible light. For e.g starting with Calcium and ending with Barium - the flame colours truly do increase in colour frequency - with Brick-red, Crimson, and Apple-green colours respectively.

    What I don't understand - if the energy gaps increase down the Group and therefore the frequency of energy along the EM spectrum increases too, why do Magnesium and Berylium (which should have the lowest energy gaps) have the highest frequencies along the EM spectrum - i.e. emitting UV light?
    Offline

    12
    ReputationRep:
    This is a really good question!

    If you look at the atomic radii of beryllium and magnesium compared to the other alkaline earth metals you'll notice that they're considerably smaller than the rest. Beryllium's is only 45pm and Magnesium's is about 70pm, compared to 100pm in calcium and about 120pm in strontium. As I'm sure you know, the decreased radii mean that the electrons are more tightly bound to the atom. This also means that the atoms' excited states are at much high energies than those of other alkaline earth metals. So when you're exciting those atoms it requires loads more energy. Then when the atoms fall back to their ground states they release this higher energy value as a photon with a higher frequency, so in these two cases UV.

    The reason that the frequencies of photons emitted by the heavier alkaline earth metals increases down the group is for the same reason. The electrons become increasingly less bound to the atom as you add more shells, so they require less energy to promote them to higher energy states. So for elements like barium you can push its electrons into some pretty high energy orbitals, much higher in energy than you can with calcium, much more easily. Therefore the frequencies of photons it emits are higher.
    Offline

    3
    ReputationRep:
    What board is this for and is it AS or A2?
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by Peroxidation)
    This is a really good question!

    If you look at the atomic radii of beryllium and magnesium compared to the other alkaline earth metals you'll notice that they're considerably smaller than the rest. Beryllium's is only 45pm and Magnesium's is about 70pm, compared to 100pm in calcium and about 120pm in strontium. As I'm sure you know, the decreased radii mean that the electrons are more tightly bound to the atom. This also means that the atoms' excited states are at much high energies than those of other alkaline earth metals. So when you're exciting those atoms it requires loads more energy. Then when the atoms fall back to their ground states they release this higher energy value as a photon with a higher frequency, so in these two cases UV.

    The reason that the frequencies of photons emitted by the heavier alkaline earth metals increases down the group is for the same reason. The electrons become increasingly less bound to the atom as you add more shells, so they require less energy to promote them to higher energy states. So for elements like barium you can push its electrons into some pretty high energy orbitals, much higher in energy than you can with calcium, much more easily. Therefore the frequencies of photons it emits are higher.
    Ahh I see, you're amazing I swear- so technically it doesn't matter how many energy levels an element originally has? - if the electrons are tightly bound to the nucleus - it can always move to very high energy levels due to their excited state, whereas if an element isn't so close to the nucleus it can already move to high energy levels because extra shells mean higher energy levels. I'm guessing this works on a two way basis - like you need a balance between a very close nucleus and high energy levels.
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by Squishy•)
    What board is this for and is it AS or A2?
    Lol it's AS but sometimes I need to learn beyond my level to understand the concept a bit more.
    Offline

    3
    ReputationRep:
    (Original post by I <3 WORK)
    Lol it's AS but sometimes I need to learn beyond my level to understand the concept a bit more.
    oh right i never learnt flame tests in AS
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by Squishy•)
    oh right i never learnt flame tests in AS
    Which exam board do you do?
    Offline

    3
    ReputationRep:
    (Original post by I <3 WORK)
    Which exam board do you do?
    AQA
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by Squishy•)
    AQA
    Ahh I see - well I do Edexcel so I guess that's what makes the difference.
    Offline

    3
    ReputationRep:
    (Original post by I <3 WORK)
    Ahh I see - well I do Edexcel so I guess that's what makes the difference.
    Oh alright then I love you sweet dreams
    Offline

    12
    ReputationRep:
    (Original post by I <3 WORK)
    Ahh I see, you're amazing I swear- so technically it doesn't matter how many energy levels an element originally has? - if the electrons are tightly bound to the nucleus - it can always move to very high energy levels due to their excited state, whereas if an element isn't so close to the nucleus it can already move to high energy levels because extra shells mean higher energy levels. I'm guessing this works on a two way basis - like you need a balance between a very close nucleus and high energy levels.
    You're close, extra shells are higher energy levels and technically all atoms have them (so long as the energy level of that shell is below the atom's first ionisation energy), though in lighter elements they're unfilled.

    When we talk about energy levels/shells and orbitals we're not actually talking about a physical thing. Orbitals are just regions of space where an electron with a particular energy can exist within the atom. We calculate what these regions look like in a 3D space using the Schrodinger equation (for hydrogen at least). The solutions of the Schrodinger equation for different quantum numbers (n = 1, 2, 3, etc) in 3D coordinate systems are the shells of atoms, with different values of l you get the different subshells and with different values of m you get the individual orbitals in those subshells. Keep in mind that these are approximations for all elements other than hydrogen.




    These energy levels and their associated energies are all dependent on the energies of the electron(s), the nuclear charge, the distance from the nucleus and a bunch of other factors, so the gaps between their energy values varies between elements. Some elements have very large energy differences between adjacent energy levels (adjacent meaning one level and then the next, they're not next to each other in the normal sense), like in Beryllium. Others have smaller gaps, like in Calcium.

    We're getting into some deep quantum physics here, sorry my explanations are a bit sloppy. I can't find my copy of the Cavendish quantum physics primer to help me out.:woo:

    Seriously though, that book is like my quantum physics bible!
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by Peroxidation)
    You're close, extra shells are higher energy levels and technically all atoms have them (so long as the energy level of that shell is below the atom's first ionisation energy), though in lighter elements they're unfilled.

    When we talk about energy levels/shells and orbitals we're not actually talking about a physical thing. Orbitals are just regions of space where an electron with a particular energy can exist within the atom. We calculate what these regions look like in a 3D space using the Schrodinger equation (for hydrogen at least). The solutions of the Schrodinger equation for different quantum numbers (n = 1, 2, 3, etc) in 3D coordinate systems are the shells of atoms, with different values of l you get the different subshells and with different values of m you get the individual orbitals in those subshells. Keep in mind that these are approximations for all elements other than hydrogen.




    These energy levels and their associated energies are all dependent on the energies of the electron(s), the nuclear charge, the distance from the nucleus and a bunch of other factors, so the gaps between their energy values varies between elements. Some elements have very large energy differences between adjacent energy levels (adjacent meaning one level and then the next, they're not next to each other in the normal sense), like in Beryllium. Others have smaller gaps, like in Calcium.

    We're getting into some deep quantum physics here, sorry my explanations are a bit sloppy. I can't find my copy of the Cavendish quantum physics primer to help me out.:woo:

    Seriously though, that book is like my quantum physics bible!
    No way your explanations are amazing! May I ask, are you some sort of Chemistry/Physics professor by any chance? :top2: On a serious note, this stuff makes so much more sense so thank you!

    Forgive me for asking a million more questions - but can we safely say that the best conditions for an element to give off energy with the highest frequency (when returning to the ground state from an excited state) should be: Having the element's electrons being close to the nucleus AND having a large difference in energy between energy levels. (E.g. Beryllium/Magnesium)

    Whereas the conditions to have a fairly high frequency (though not as high as the condition above) could be the case where an element would have a much lower energy difference between energy levels, yet because the electrons have already filled higher energy shells the resultant frequency of the photons released would be high. (E.g. Strontium/Barium)
    Offline

    3
    ReputationRep:
    woah i am studying A2 physics and chem and all this stuff looks so hard
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    What's your favourite Christmas sweets?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.