Atomic Absorbances and Emissions

Question 1

The electromagnetic spectrum

Answer 1

The electromagnetic spectrum shows the wavelengths of electromagnetic waves, ranging from gamma rays with wavelengths. Since electromagnetic radiation has a fixed speed (speed of light), these wavelengths have an associated energy and frequency according to the equations.

Question 2

Energy Level Diagrams

Answer 2

Electrons in atoms can move between energy levels. An electron will absorb energy to move to a higher energy level (producing an excited state), and when the electron emits energy it will drop down to a lower level. The electron must absorb exactly the correct energy to move between energy levels, which means that it must absorb a photon of the correct wavelength. No elements have the same energy gaps between energy levels.

Question 3

Emission vs absorption spectra

Answer 3

Since atoms of different elements have different energy gaps between their energy levels, atoms of different elements can be identified by looking at wavelengths that they absorb and re-emit.

Question 4

Emission Spectra of Hydrogen

Answer 4

Hydrogen has four lines in the visible spectrum, but also has lines in the non-visible spectrum.

Question 5

Flame Tests

Answer 5

Elecrons in atoms can be excited (promoted to a higher energy level) by strong heating. As the elcectrons fall back down to the ground state they release energy. If this energy is in visible range it will produce a characteristic colour for the element.

Question 6

Atomic Absorption Spectroscopy

Answer 6

This technique is used to identify the concentration of a specific ion in solution. It’s based on the idea that the more atoms present, the more photons of a specific wavelength will be absorbed. The sample is vapourised and heated in the burner, then irradiated with a specific wavelength of light. Some of the energy is absorbed by the sample, and the difference between energy before and after it passes through the sample (absorbance) is detected.

Question 6

Atomic Absorption Spectroscopy

Answer 6

This technique is used to identify the concentration of a specific ion in solution. It’s based on the idea that the more atoms present, the more photons of a specific wavelength will be absorbed. The sample is vapourised and heated in the burner, then irradiated with a specific wavelength of light. Some of the energy is absorbed by the sample, and the difference between energy before and after it passes through the sample (absorbance) is detected.

Question 7

Determining Concentration using AAS

Answer 7

The amount of energy absorbed vby the atom at a specific wavelength corresponds to the number of atoms int he sample and can be used to determine the concetration. This is usually done by preparing a calibraton curve and standard solutions, and then analysing the unknown solutions. Extrapolation is not a valid technique.

Question 8

Mass Spectroscopy

Answer 8

The masses of different isotopes and their relative abundaces can be measured using a mass spectroscopy.

1. Atom/molecule is ionized to produce a positive ion.
2. Ions are accelerated towards a negatively charged plate.
3. The accelerated ions are deflected by a magnetic field based on their mass and charge (m/z). We assume the ions are all 1+, so ions with a small mass can be deflected more than heavier ions.
4. The positive ions are detected which creates a signal.

Question 9

Analysing mass spectra

Answer 9

Since mass spectrometry alows us to measure the relative abundances of isotopes, we can use it to determine relative atom masses.

Question 10

Determining Relative Atomic Masses

Answer 10

((atomic mass * %)/100) + ((atomic mass * %)/100)