WHy do different elements produce colours in flame test? (1 Viewer)

[.ben]

Is is becausethe electrons become excited jum p and fall the n release energy?

Also how can you tell which colour it produces on an emission sprectrum? is it by looking at most dominant colour?>

Finally, how do you describe an emission spectrum? do you just list the wavelengths and colours present?

thnz

 

[passion89]

Is is becausethe electrons become excited jum p and fall the n release energy?

Yes, they release and emit energy at certain frequencies, which is what gives the spectra different colours. For eg: Copper's frequency would be different (and consequently a different colour) to Calcium.

Finally, how do you describe an emission spectrum? do you just list the wavelengths and colours present?

An emission spectrum shows coloured lines on a black background (and absortion is the opposite). The spectrum can be analysed and described by seeing which line/colour/frequency is present on the black background so basically, yes.

 

[tristambrown]

I dont do the Forensic chem elective so i'll just give you a straight quote that i think covers yur q. All of this is way above the scope of chemical monitoring & management though if that is what u need it for .

According to rolland smith in 'conquering chemistry 4th edition'

regarding AES

"if we heat atoms to a high temperature, some of the electrons getexcited out of their normal energy levels into higher energy levels. However after a short period of time these electrons fall back from these higher energy levels to the normal levels. As they do this the excess energy is liberated as light (either visable or uv). The energy emitted as an electron falls back to its normal(ground)state is the same as that absorbed when it was raised to the excited state. If we break the emitted light into its varuious wavelength components (by padding it through a prism), we fins that the emissions have occured at just a few discrete wavelengths as shown .in fig 6.12. The pattern of lines (wavelengths) is called an emission spectrum of the element(a set of bright or coloured lines on a black background). Each wavelength corresponds to the energy required to excite a particular electron in the atom from its ground state to an excited state and back to the ground state. Each element has its own unique emission spectrum. ... By measuring the emission spectrum of a sample and comparing it with the known spectra of elements we can identify the elements present in the sample. Measuring, studying anf using such spectra is called Atomic emission spectroscopy. It is exctremly usedul for qualitatively identifying elements present in samples"

 

[angmor]

Is the AES in the syllabus?

 

[Riviet]

Is the AES in the syllabus?

Don't think so, but AAS is.

 

[onebytwo]

"why do different elements produce different colours in flame tests"
i thought it was basically because certain atoms/ions have differing distances between electron energy shells. so when an excited electron falls back from its excited state it produces energy of a different frequency, thus different coloured light

btw, whats AES?

 

[Riviet]

AES stands for Atomic Emission Spectroscopy.

 

[tennille]

AES is very similar to AAS (atomic absorption spectroscopy), however, in AES we are analysing the emission lines, which is specific for each element. There is a source, such as a flame, which excites the atoms resulting in emission. AES is used to determine what the components of the sample are. In AAS, there is a source of light which consists of the same wavelength as the sample will absorb, which would result in the excitation of that sample. Basically, it measures the amount of light that is absorbed by the sample, which is dependent on the concentration of the sample. So AAS is used to determine the concentration of a sample.

 

[.ben]

ok but why do different elements produce diferent wavelengths when the electrons in their shells are at teh same level. E.g. boron and carbon both have electrons in their 2nd sheelsls.

 

[Tim035]

The energy of the absorbed light used to promote electrons to higher energy levels corresponds with the difference in the energy between the two energy levels the electron moved between.
Since each atom has its own unique set of energy levels in its atoms, the frequency of light emitted by a sample of an element will be unique an characteristic of that element.

So more straight forward, even though they may have electrons in the same shells, the energy levels between the different shells in the atom will not be the same for boron and carbon.

Lol I think I said energy about 5 times in that small paragraph.

 

[.ben]

nah i still don't get it

So more straight forward, even though they may have electrons in the same shells, the energy levels between the different shells in the atom will not be the same for boron and carbon.

why are the energy levels between the different shells in the atom not the same for differente elements?

 

[.ben]

When electrons are excited in their respective atoms, they will jump to higher energy levels. However, these varies from atom to atom and electron to electron as differing atoms have different energy values for different shells and also differing electrons will be excited differently. For example using atom X, its electron A might be at level 4 after excitation, while atom X's other electron, electron B might be only at level 3. When de-excitation occurs, electron B might drop down to level 2 while, electron A might drop down to level 1. Thus from the energy-wavelength formula, we can deduce the exact wavelength that is emitted when atom X's electrons are excited. Different atoms will have different excitations and de-excitations and thus will produce wavelengths specific to its properties.

is this correctr?

 

[Tim035]

Yep

Are you doing forensics??? If not ur troubling yourself ALOT over nothing.

Also remember the electrons don't fall all the way back down to ground state straight away, they may fall to several lower electrons shells b4 finally resting on ground level. Otherwise in an emision spectrum atoms would just have one Definite line each.