Electromagnetic radiation and atomic spectra Flashcards
What is the electromagnetic spectrum ?
The different types of radiation arranged in order of wavelength is known as the electromagnetic spectrum.
What does dual nature mean ?
Electromagnetic radiation can be described as a wave (has a wavelength and frequency), and as a particle, and is said to have a dual nature.
Frequency is often quoted in Hz, which is the same as s^-1
What is a photon ?
-When electromagnetic radiation is absorbed or emitted by matter it behaves like a stream of particles. These particles are known as photons.
-A photon carries quantised energy proportional to the frequency of radiation.
-When a photon is absorbed or emitted, energy is gained or lost by electrons within the substance. (absorbed = gains, emitted = lost)
What happens when energy is transferred to an atom ?
-When energy is transferred to atoms, electrons within the atoms may be promoted to higher energy levels.
-An atom emits a photon of light energy when an excited electron moves from a higher energy level to a lower energy level
-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 provides direct evidence for the existence of these energy levels.
What can spectra be used for ?
Each element in a sample produces characteristic absorption and emission spectra. These spectra can be used to identify and quantify the element.
(intensity of transmitted/absorbed radiation is proportional to the quantity of atoms/ions in sample)
Describe how an absorption spectrum is produced
-In absorption spectroscopy, electromagnetic radiation is directed at an atomised sample. Radiation is absorbed as electrons are promoted to higher energy levels.
-An absorption spectrum is produced by measuring how the intensity of absorbed light varies with wavelength.
-In atomic spectroscopy, the concentration of an element within a sample is related to the intensity of light emitted or absorbed
Describe how an emission spectrum is produced ?
-In emission spectroscopy, high temperatures (or electical discharge) are used to excite the electrons within atoms.
-As the electrons drop to lower energy levels, photons are emitted.
-An emission spectrum of a sample is produced by measuring the intensity of light emitted at different wavelengths.
-In atomic spectroscopy, the concentration of an element within a sample is related to the intensity of light emitted or absorbed.
What is the significance of a line spectrum ?
Each line reresents the movement of an electron from one energy level to another.
It suggests that elecrons can only occupy certain fixed energy levels.
