Unit 1 ) 2) Atomic Emission And Atomic Absorption

Question 1

What happens when white light is passed through a prism

Answer 1

• When white light is passed through a prism a rainbow effect is seen- this is known as the continuous spectrum and includes all the colours in the visible part of the electromagnetic spectrum (from about 400-700nm)

Question 2

• What happens when atoms absorb light energy

Answer 2

When atoms absorb light energy the electrons become excited and are promoted to higher energy levels (after absorbing a photon )
- eventually the electron will fall back to ground state - when they fall back down, they emit light energy

Question 3

Where an electron gets excited to depends on….

Answer 3

…how much energy is absorbed
- the electrons could be promoted to third, fourth,fifth energy level : where it gets excited to depends on how much energy is absorbed

Question 4

What happens if an atom absorbs a high amount of energy

Answer 4

• if an atom absorbs a high amount of energy , it is emitted becoming ionised

Question 5

Each individual electron transition will emit light with an energy that is specific to that ______

Answer 5

Each individual transition will emit light with an energy that is specific to that transition

Question 6

Explain atomic emission spectra

Answer 6

• when a beam of white light is passed through a prism , a continuous spectrum is visible
• when white light from a source passes through a sample being heated/ a substance , the spectrum turns out not to be a continuous spectrum but a series of lines of different wavelengths and thus different colours.
• Each line corresponds to the energy given out when excited electrons move down to a lower energy level , generating photons of various frequencies.

Question 7

What do the lines in atom emission spectra correspond to

Answer 7

These lines correspond to certain specific frequencies and wavelengths found in the visible or ultraviolet spectrum
- each element creates its own unique spectrum , something like a chemical fingerprint , with its own specific frequency and wavelengths

Question 8

Explain atomic absorption spectroscopy

Answer 8

• when a beam of continuous radiation like white light is directed through a gaseous sample : it can cause an atom to make a transition from its ground state to its excited state.
• if the frequency of the light , and therefore the energy of the photon , corresponds to an excitation energy of the atom , then a photon of light is absorbed
• the radiation will therefore have certain wavelengths missing. These show up as dark lines on a continuous spectrum called an atomic absorption spectrum

Question 9

• An emission spectrum of a sample is produced by measuring…

- An absorption spectrum is produced by measuring….

Answer 9

• An emission spectrum of a sample is produced by measuring the intensity of light emitted at different wavelengths.
• An absorption spectrum is produced by measuring how the intensity of absorbed light varies with wavelength

Question 10

In atomic spectroscopy, the _______ of an element within a sample is related to the intensity of light emitted or absorbed.
So:
In absorption spectroscopy, as the concentration of an ion in solution increases, there is an increase in the _______ of radiation _____

Answer 10

In atomic spectroscopy, the concentration of an element within a sample is related to the intensity of light emitted or absorbed.
- increase in intensity of radiation absorbed.

Question 11

What can emission and absorption spectroscopy be used for

Answer 11

• they can be used to determine whether a certain species is present in a sample and how much of it is present , since the intensity of the transmitted or absorbed radiation can be measured