photoemission & energy levels Flashcards
`What happens to electron energies as it moves closer to the nucleus?
decreases
State what is meant by the ground state energy.
when an atom is at its lowest energy state
State what is meant by the ionisation energy.
the minimum energy required to ionise an atom in its ground state
State the meaning of the term excitation.
when electrons move to a higher energy level
How much energy is absorbed from a free electron to excite an electron?
the exact amount required.
What happens to the leftover energy of a free electron ?
remains part of the free electron
State the meaning of the term de-excitation.
when an electron moves from a higher energy level to a lower one
What happens when electrons de-excite?
they release energy in the form of photons
When do atoms absorb photons?
when they have the exact amount of energy required for an electron to move across energy levels
Describe the difference between excitation by photons and excitation by electrons.
→ e-: can transfer part of their energy and move away with leftover
→ photons: only absorbed if energy is exactly equal to that required
State the energy required for ionisation by photons. What happens to the leftover energy?
→ must be greater than ionisation energy
→ leftover energy = kinetic energy of new free electron
From left to right, what happens to the frequency and wavelength along the electromagnetic spectrum?
→ frequency increases
→ wavelength decreases
In the visible light spectrum, which colour has the longest wavelength?
red
Describe how to study the light emitted by excited hydrogen gas.
→ 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
What is the emission spectra?
spectrum of light displayed when atom emits light due to the emission of photons
What does each line on an emission spectrum represent?
→ a wavelength of light
→ associated with different colours
→ in visible region of electromagnetic spectrum
What does an emission spectrum diagram represent?
different wavelengths of light that are observed when atoms are de-excited
What were emission spectra evidence for?
→ energy transmissions that occurred within an atom
→ allowed physicists to model the energy levels of an atom
Explain how a fluorescent tube works.
→ 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)
Describe what an absorption spectrum looks like.
a continuous spectrum containing all colours with dark lines at certain wavelengths
Explain how an absorption spectrum is produced.
→ 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
State how a continuous spectrum is produced.
light emitted by atoms in a solid, a liquid or a gas at high pressure
