photoemission & energy levels

Question 1

`What happens to electron energies as it moves closer to the nucleus?

Answer 1

decreases

Question 2

State what is meant by the ground state energy.

Answer 2

when an atom is at its lowest energy state

Question 3

State what is meant by the ionisation energy.

Answer 3

the minimum energy required to ionise an atom in its ground state

Question 4

State the meaning of the term excitation.

Answer 4

when electrons move to a higher energy level

Question 5

How much energy is absorbed from a free electron to excite an electron?

Answer 5

the exact amount required.

Question 6

What happens to the leftover energy of a free electron ?

Answer 6

remains part of the free electron

Question 7

State the meaning of the term de-excitation.

Answer 7

when an electron moves from a higher energy level to a lower one

Question 8

What happens when electrons de-excite?

Answer 8

they release energy in the form of photons

Question 9

When do atoms absorb photons?

Answer 9

when they have the exact amount of energy required for an electron to move across energy levels

Question 10

Describe the difference between excitation by photons and excitation by electrons.

Answer 10

→ e-: can transfer part of their energy and move away with leftover
→ photons: only absorbed if energy is exactly equal to that required

Question 11

State the energy required for ionisation by photons. What happens to the leftover energy?

Answer 11

→ must be greater than ionisation energy
→ leftover energy = kinetic energy of new free electron

Question 12

From left to right, what happens to the frequency and wavelength along the electromagnetic spectrum?

Answer 12

→ frequency increases
→ wavelength decreases

Question 13

In the visible light spectrum, which colour has the longest wavelength?

Answer 13

red

Question 14

Describe how to study the light emitted by excited hydrogen gas.

Answer 14

→ discharge tube with low pressure gas
→ electrons are accelerated using a voltage supply and a +ive plate
→ e- collide with H atoms causing excitation and de-excitation
→ photons of certain wavelength are released

Question 15

What is the emission spectra?

Answer 15

spectrum of light displayed when atom emits light due to the emission of photons

Question 16

What does each line on an emission spectrum represent?

Answer 16

→ a wavelength of light
→ associated with different colours
→ in visible region of electromagnetic spectrum

Question 17

What does an emission spectrum diagram represent?

Answer 17

different wavelengths of light that are observed when atoms are de-excited

Question 18

What were emission spectra evidence for?

Answer 18

→ energy transmissions that occurred within an atom
→ allowed physicists to model the energy levels of an atom

Question 19

Explain how a fluorescent tube works.

Answer 19

→ glass tubes filled with low-pressure mercury vapour with a phosphor coating on the glass
→ electric current is passed through vapour, e- in mercury are excited & move to a higher energy level
→ e- de-excites, releasing energy in the form of UV photons
→ this energy cause e- in the phosphor to excite & de-excite, releasing visible light (fluorescent glow)

Question 20

Describe what an absorption spectrum looks like.

Answer 20

a continuous spectrum containing all colours with dark lines at certain wavelengths

Question 21

Explain how an absorption spectrum is produced.

Answer 21

→ white light passes through a cool, low pressure gas
→ excitation of e- due to absorption of photons
→ e- then de-excite & photons are released in all directions ∴ some λ appear to be missing

Question 22

State how a continuous spectrum is produced.

Answer 22

light emitted by atoms in a solid, a liquid or a gas at high pressure