3.4 Energy levels in atoms

Question 1

What is the ground state?

Answer 1

» The lowest energy state of an atom

Question 2

What does it mean if an electron is an excited state?

Answer 2

» Electron gains energy higher than its ground state

Question 3

What is de-excitation?

Answer 3

» The electron emits a photon and moves to a lower energy level

Question 4

What is the energy of the photon equal to?

Answer 4

» The energy lost by the electron therfore, by the atom

Question 5

What is the equation of an emitted photon equal to?

Answer 5

» E1 - E2

Question 6

When will the electron move to an outer shell where a vacancy exists?

Answer 6

» If the energy of the photon is equal to the gain in the electrons energy
» The photon energy must be exactly equal to the difference between the final and initial energy levels of the atom

Question 7

When can a photon cause ionisation?

Answer 7

» If its energy is greater than or equal to the difference between the ionisation level and ground state

Question 8

Why do certain substances fluoresce or glow with visible light when the absorb uv radiation?

Answer 8

» Atoms absorb uv photons and become excited
» When atoms de-excite they emit visible atoms

Question 9

What is a fluorescent tube?

Answer 9

» Glass tube with a fluorescent coating on its inner surface

Question 10

What does a florescent tube contain?

Answer 10

» Mercury vapour at low pressure

Question 11

Why does a fluorescent tube emit light?

Answer 11

» Ionisation and excitation the mercury atoms occur as they collide with each other and with electrons in the tube
» Mercury atoms emit uv photons as well as visible light photons, when they dexcite
» UV photons are absorbed by the special powder in the coating
» Causing excitation of the atoms
» The coating atoms de-excite in steps and emit visible photons

Question 12

What is the purpose of the coating on the inside surface of the glass in the fluorescent tube?

Answer 12

» Coating absorbs UV light
» Causes the Coating to become excited
» Powder absorbs and emits photons in the visible light spectrum when it de-excites
» Incident photons have variety of wavelengths, photons are emitted with continous wavelengths, which are visible

Question 13

What happens to an electron in the ground state when it receives radiation of a frequency greater than the minimum frequency?

Answer 13

» The frequency is greater
» Energy of the electron is greater
» Greater maximum kinetic energy
» Therefore leaves the atom

Question 14

When can excitation happen?

Answer 14

» If electron absorbs of photon of exactly the right energy
» If another electrons hits it, donating some of its kinetic energy to move the atomic electron

Question 15

How can collision of charged particles inside a gas atom can cause the atom to emit photons?

Answer 15

» Collison of gas particles causes transfer of energy to the electrons in the gas atom
» Electrons excite to a higher level
» They are unstable, so fall down an energy level and emit a photon

Question 16

How are spectral lines explained by the concept of discrete energy levels?

Answer 16

» Photon energy = hf
» Spectral lines have specific wavelengths
» They are formed as an electron falls down to a lower energy level

Question 17

In terms of electrons, explain 2 differences between excitation and de-excitation?

Answer 17

» Energy of electron increases in excitation and decreases in de-excitation
» Excitation can occur in photon or electron absorption
» De-excitation only occurs through photon emission

Question 18

Explain why atoms in a fluorescent tube stops emitting light when the electricity supply to it is switched off?

Answer 18

» Excitation by collision of the gas atoms with the electron stops
» Therefore mercury atoms do not longer emit uv radiation and so coating atoms do not longer emit light

Question 19

Describe the process which mercury atoms become excited in a flurescent tube?

Answer 19

» Mercury atoms collide with electrons when power is turned on
» Causes mercury atom to excite
» As they gain kinetic energy from the electrons