Energy Levels & Photon Emission ( 3 )

Question 1

What is a key feature of the wavelengths of lines of a line spectrum of an element?

Answer 1

• Wavelengths of the lines of a line spectrum of an element are characteristic of the atoms of that element.
• By measuring the wavelengths of a line spectrum, you can identify the element that produced the light.
• No element produces the same pattern of light wavelengths.

Question 2

How can you identify element that produces a particular light?

Answer 2

• Wavelengths of the lines of a line spectrum of an element are characteristic of the atoms of that element
• By measuring the wavelengths of a line spectrum, you can identify the element that produced the light.
• No element produces the same pattern of light wavelengths.

Question 3

Why is the pattern of light wavelengths unique to an element?

Answer 3

• Energy levels of each type of atom are unique to that atom.
• So photons emitted are characteristic of the atom.

Question 4

What is the line in a line spectrum caused by?

Answer 4

• Each line in a line spectrum is due to light of a certain colour, and therefore a specific wavelength too.

Question 5

How can the energy of an emitted photon be worked out?

Answer 5

• Photons that produce each line all have the same energy, which is different from the energy of the photons that produce any other line.
• Each photon is emitted when an atom de-excites due to one if its electrons moving to an inner shell.
• If the electron moves from energy level E1, to a lower energy level E2:
• Energy of emitted photon, hf = E1 - E2

Question 6

What occurs if you split light from a fluorescent tube?

Answer 6

• If you split light form a fluorescent tube with a prism or diffraction grating, a line spectrum forms.
• A line spectrum is seen as a series of bright lines against a black background.

Question 7

What does each line correspond to in a line emission>

Answer 7

• A particular wavelength of light emitted by the source.

* Since only certain photon energies are allowed, you only see the wavelengths corresponding to these energies.

Question 8

What is white light?

Answer 8

A continuous spectra.

Question 9

What occurs if you split white light with a prism?

Answer 9

• All colours merge into each other, no gaps are present.

Question 10

Why are all wavelengths allowed in continuous spectra?

Answer 10

• Electrons are not confined to energy levels in the object producing the continuous spectrum.
• Electrons are not bound to atoms and are free

Question 11

When do you get a line absorption spectrum?

Answer 11

When light with a continuous spectrum of energy ( e.g. white light ), passes through a cool gas.

Question 12

What is the state of electrons at low temperatures?

Answer 12

Most electrons in the gas atoms will be in their ground states.

Question 13

What happens when a light with a continuous spectrum passes through a cool gas?

Answer 13

• Photons of the corresponding wavelengths are absorbed by the electrons to excite them to higher energy levels.
• These wavelengths are missing from the continuous spectrum when it comes out the other side of the gas
• A continuous spectrum with black lines in it corresponding with the absorbed wavelengths are absorbed
• If absorption and emission spectra of a particular gas are compared, the black lines in the absorption spectrum match up the bright lines in the emission spectrum.