Particles and radiation

Question 1

What are energy levels and which one do electrons occupy?

Answer 1

• Electrons in an atom occupy certain energy states known as energy levels
• Electtons will occupy the lowest possible energy level as this is the most stable configuration for the atom

Question 2

What happens to an electron when it absorbs or emits a photon?

Answer 2

• The electron can move between energy levels, or be removed from the atom completely

Question 3

What is excitation?

Answer 3

• When an electron absorbs enough energy to move up an energy level

Question 4

When is an atom in an excited state?

Answer 4

• When an electron within the atom absorbs a photon and moves up an energy level

Question 5

What must be done to excite an electron?

Answer 5

• The electron must absorb a photon

Question 6

How do electrons de-excite?

Answer 6

• Electrons can move down energy levels by de-excitation
• To do this, the electron must emit a photon

Question 7

What is ionisation?

Answer 7

• Ionisation is when an atom gains or loses an orbital electron and becomes charged

Question 8

What is the ionisation energy and which electron can be removed?

Answer 8

• An electron can be removed from any energy level it occupies
• The ionisation energy is the minimum energy required to remove an electron from the ground state of an atom

Question 9

When does flourescence occur?

Answer 9

• Flourescence occurs when an electron in an atomic oribital absorbs energy from an interaction with a photon or a collision with another electron

Question 10

What are flourescent bulbs made of?

Answer 10

• They are partially evacuated glass tubes filled with low-pressure mercury vapour with a coating of phosphor on the glass

Question 11

How do flourescent tubes work?

Answer 11

• When a high voltage is applied across the tube, eelctrons flow from the cathode to the anode producing an electron beam
• These beam electrons collide with the electrons in the emrcury atoms transferring kinetic energy in collision
• The atomic electrons in the mercury atoms are excited and move to higher energy levels
• The high-energy level state is unstable to the electrons de-excite and move back down to their original ground state
• As they de-excite, they release this energy by emitting photons in the UV range of wavelengths
• The UV photons then collide with the electrons in the atom of the phosphor coating and excite them into higher energy levels
• As the phosphor electrons de-excite, they do so by emitting photons in the visible light range of wavelengths

Question 12

Why do we use electronvolts?

Answer 12

• The electronvolt is a unit commonly used to express very small energies
• This is because quantam energies tend to be much smaller than 1 joule

Question 13

What is 1 eV?

Answer 13

• If an electron, with a charge of 1.6 x 10^-19, travels through a potential difference of 1V, the energy transferred is equal to:
• E = QV = 1.6 x 10^-19

Question 14

How do you convert from eV to J and back?

Answer 14

• eV to J : multiply by 1.6x10^-19
• J to eV : divide by 1.6 x 10^-19

Question 15

What is an electronvolt?

Answer 15

• The energy gained by an electron travelling through a potential difference of one volt

Question 16

How is an electronvolt related to kinetic energy?

Answer 16

• When a charged particle is accelerated through a potential difference, it gains kinetic energy. If an electron accelerated from rest, an electronvolt is equal to the kinetic energy gained
• eV = 0.5 x m x v^2

Question 17

How do you calculate electronvolts?

Answer 17

• eV = e x V
• eV = charge of electron x potential difference
• 1eV = 1.6 x 10^-19 J