Atomic Spectroscopy Flashcards
What spectrum does visible light belong too?
Electromagnetic radiation
What is an oscillation?
An oscillation is a wave like property that occurs in regular variations.
What is frequency?
Frequency is how many times the wave crests per second.
What is frequency measured in?
Hertz (Hz) with a unit of reciprocal seconds
What is a wavelength?
A wavelength is the distance between two crests of a oscillation. Wavelength is denoted by Lambda λ and is measured in meters.
What does the product of wavelength and frequency produce?
The speed of light (C (ms-1)).
If speed of light is constant in a vacuum, what does that imply about the relationship between wavelength and frequency?
That they are inversely proportional.
What is amplitude?
Amplitude is the displacement of the wave from the central point, therefor it is half of the total movement.
What property is amplitude responsible for in light?
It is responsible for the intensity of a light, not to be confused with energy of light. Higher amplitude = brighter light.
How do we calculate the energy of a wavelength?
To get the energy of a wavelength with multiply Planck’s constant (h) by the frequency of the wave (v) . E = h v
What is Planck’s constant and its unit?
Planck’s constant is 6.626 x 10-(34) and it is measured in Joules per second.
How do we get the unit of energy using E = h v?
If h is joules per second and frequency is measured in reciprocal seconds then we get E = Joules.
How does an increase of frequency appear on the electromagnetic spectrum?
An increase in frequency will correspond to a shorter wavelength and a higher energy. Higher frequency will move towards gamma rays, whilst lower frequency will move towards radio waves.
What is a broadband?
It is the collection of a range of frequencies. An example would be white light which is a collection of all visible light spectra.
What are the two possible effects that the absorption of energy can have on electrons?
Ionisation and Transition.
Ionisation is when a large enough energy can completely dissociate an electron from a nucleus. Transition is where a smaller energy is absorbed by the electron and it is transitioned into a higher state.
What is common in excited electrons?
These electrons will readily give up their excess energy so that they can fall back down to ground state.
How can an electron lose its excess energy?
It can either emit light (Fluorescence) or it can lose it in collisions to other molecules/atoms (Heat).
What is a fluorescent material?
It is a material that can absorb higher energy UV light and then re emit at a lower frequency which is the visible light.
How do we get an absorption spectrum?
We get it by subjecting a gas substance of interest with a full visible light broadband. The resulting black marks on a spectroscope determines the frequencies absorbed.
what is an emission spectrum?
It is when a gas discharge tube excites a gas of interest in a visible light absent environment. by passing the emitted light discharge through a prism we can determine the frequencies released.
Why is absorption and emission spectra useful?
Because each element has its own unique frequency characteristics which can then help with identification.
Why is the emission and absorption spectra of atoms quantised?
As the spectra can only have absolute specific values. This is because the electrons are restricted to specific energy states.
How many electrons can an orbital accomodate?
An orbital can either contain 0 , 1 or 2 Orbitals.
What does orbitals have to do with absorption and emission spectra?
Orbitals are the quantised energy levels that predefined how electrons get excited or emit. When an electron is excited it gets promoted to a higher orbital and vice versa.
What is a limitation of Atomic Absorption/Emission Spectroscopy?
It is fairly limited to atoms, as molecules are too complex. It is generally reserved for trace elements.
In terms of data, does AAS or AES provide more data points?
Atomic emission spectroscopy provides more data as the emission pathway between orbitals has a greater variation the the absorption spectroscopy. More Data lines is AES.
How do we using atomic spectroscopy on elements that have combined with others?
We use atomisation to destroy any molecules and leave nothing but elements to be used in spectroscopy.
What are the steps of flame AAS?
1) Prepare a solution using a solvent. (Typically Water)
2) Nebulise the solution into tiny droplets
3) Desolvation to evaporate the solvent
4) vaporisation of the compound to produce a gas
5) atomisation of the gas to product a neutrally charged atom.
6) the excitation of the analyte
How do we interpret data from flame AAS?
Flame AAS measures the quantity of analyte present by investigating the decrease of intensity of light. This is measured by passing light through the analyte flame.
How do we ensure that we are measuring the correct element?
We only use wavelengths specific to the elements absorption band as a light source.
how do we ensure that a specific light wavelength is used as the incident light on the flame in flame AAS?
We use a monochromator to filter out unwanted wavelengths.
What does beer-lamberts law suggest in regards to flame AAS?
That the comparison of incident light to the absorbed light can determine the quantity of analyte.
What is beer lamberts law?
Absorbance = Log( Incident Light / After Incident Light) = Molar absorbity x Path length of flame x concentration of analyte
A = Log( Io / I ) = abc
What is electrothermal AAS?
Electrothermal AAS is the same as flame AAS, however instead of using flame, heat is generated electrically in increasing stages. These increase until the element analyte is released into a gas form.
What is the advantage of electrothermal AAS?
It allows form any state of analyte to be tested (Solid, liquid, Gas)
what is the disadvantage of electrothermal AAS?
Higher costs and lower throughputs.
In order to confirm the accuracy of aborbance measures what do we need to do?
We need to create a calibration curve that allows us to compare where Beer-lambert law remains linear. By using the calibration curve we can dilute our analyte if necessary to ensure we are getting an accurate reading.
What maximum value of absorbance should we take as accurate?
An absorbance value of 1.5
What is ICP-OES
This is Ion coupled plasma spectroscopy.
By using a argon based plasma as a excitation source we can near completely atomise the analyte which will give a more accurate result.
What are some practical considerations of spectroscopy?
AS we are measuring for trace elements it is essential that we use analytical grade chemicals and reagent blanks in our research.
As there is many factors that can affect the analysis from atomisation, nebulisation, flame, etc. we need to run frequent standards.
