Collisions of Electrons with Atoms

Question 1

what is meant by excitation?

Answer 1

• when an electrons absorbs enough energy to move up to a higher energy level

Question 2

what is meant by an excited state?

Answer 2

• a state in which an atom contains an electron that has been excited

Question 3

how can electrons move back down to a lower energy level?

Answer 3

de-excitation

Question 4

what is meant by ionisation?

Answer 4

• when an atom gains or loses an electron and becomes charged

Question 5

what is meant by ionisation energy?

Answer 5

• minimum energy required to remove an electron from the ground state of an atom

Question 6

give the first three steps of how a FLUORESCENT TUBE WORKS

Answer 6

• high voltage applied, electrons flow from the cathode to the anode, producing an electron beam

• this electron beam collides with mercury electrons transferring kinetic energy in collisions

• atomic electrons in mercury atoms are excited and move to a higher energy level

Question 7

give the final four steps of how FLUORESCENT TUBES work

Answer 7

• the higher energy level is unstable so electrons de - excite back to ground state

• as they de-excite, energy is released in form of photons in UV range of wavelengths

• UV photons collide with electrons in atoms of phosphur coating and excite them

• as these phosphor electrons de - excite, they do so in stages emitting photons in visible light ranges

Question 8

explain what is meant by an emission spectra

Answer 8

• when an electrons transitions from a higher to a lower energy level it emits a photon
• each transition corresponds go a different wavelength, as pE = hf
• emission spectrum contains a set of coloured lines on a black background

Question 9

what does emission specta provide evidence for?

Answer 9

• the fact that electrons in atoms can only transition between discrete energy levels.

Question 10

what is meant by an absorption spectra

Answer 10

• an atom can be raised to an excited state by the absorption of a photon
• when white light was passes through a cool, low pressure gas it is found that light of certain wavelengths are missing

• spectrum consists of every colour of light containing black lines due to absorption of thatwavelength

Question 11

how do you calculate the difference in discrete energy levels?

Answer 11

change in energy level = hf