Spectra
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order of the EM spectrum low->high energy high->low wavelength low->high frequency
Radio Micro Infrared Visible UV X-Ray Gamma
What can EM radiation be described as?
a wave and as a particle (dual nature)
What does EM radiation behave as when emitted or absorbed by matter?
stream of particles-photos
What does a photon carry?
quantised energy proportional to the frequency of radiation
What happens to electrons within a substance when photons are absorbed or emitted?
They gain or lose energy
Which photons transfer greater amounts of energy- those in high or low frequency radiation?
high
What happens to electrons when energy is transferred to atoms? (and how do we excite atoms?)
They may be promoted to higher energy levels (We excite atoms when we heat them up (eg bunsen burner) then they absorb this heat energy)
When does an atom emit a photon of light?
When an excited electron moves from a. higher energy level to a lower energy level.
How are spectra produced and what are they direct evidence for?
The light energy emitted by an atom produces a spectrum that is made up of a series of lines at discrete (quantised) energy levels. This provided direct evidence for the existence of these energy levels
What can spectra be used to do?
Identify and quantify an element as each element in a sample produces characteristic absorption and emission spectra.
What happens in absorption spectroscopy and how is an absorption spectra produced?
-electromagnetic radiation is directed at an atomised sample. Radiation is absorbed as electrons are promoted to higher energy levels -It is produced by measuring how the intensity of absorbed light varies with wavelength
What happens in emission spectroscopy and how is an emission spectra produced?
-high temperatures are used to excite the electrons within atoms. As the electrons drop to lower energy levels, photons are emitted (absorbed by a gas) -Produced by measuring how the intensity of light emitted varies wavelength
In atomic spectroscopy, what is the concentration of an element within a sample related to?
the intensity of light emitted or absorbed
What are the highest energy lines caused by in spectra?
the largest transitions (lines in the UV area)
What happens to energy levels as they get further from the nucleus? + effect on emission spectra?
they get closer together (lines on emission spectrum get closer together and converge)
What is the energy difference between ground state and the convergence limit called?
ionisation energy
What is the intensity of the light related to?
the concentration of the element present
In absorption spectroscopy, what happens as the concentration of compound increases?
the intensity of radiation absorbed increases but the intensity transmitted will decrease