How are electrons arranged in atoms?
Electrons are arranged in ‘shells’ around the nucleus which increase in energy per electron by discrete amounts further from the nucleus
How do electrons move between different shells?
Electrons can move between shells by absorbing energy (excitation) or releasing energy (spontaneous emission) usually in the form of photons
What is ionisation and when does it occur?
Ionisation is process where atoms gain or lose electrons and occurs when electrons absorb enough energy to be removed from the atom entirely
What are line spectra?
Line spectra are patterns of bright or dark lines occurring when atoms emit or absorb light and this light is passed through a prism or diffraction grating and spread out of wavelength which corresponds to different colours
What are emission spectra?
Emission spectra occur when electrons transition from a higher to lower energy level when they emit a photon - this results in line spectra containing a set of discrete wavelengths represented by coloured lines on a black background
How do you calculate the change in energy of a photon?
ΔE = hf = hc/λ
ΔE = change in energy level (J)
h = Planck’s constant (J s)
f = frequency of photon (Hz)
c = the speed of light (m s-1)
λ = wavelength of the photon (m)
What are absorption spectra?
Absorption spectra occur when an atom is excited by the absorption of photons - it consists of a continuous spectrum containing all the colours with dark lines at certain wavelengths - these lines correspond exactly to the differences in energy levels in an atom - When these electrons return to lower levels, the photons are emitted in all directions, rather than in the original direction of the white light
Therefore, some wavelengths appear to be missing
Absorption spectra occur when an atom absorbs photons - resulting in line spectra containing dark lines on a bright background corresponding to the difference in energy level in an atom
Does light act as particles or waves?
Light both behaves like particles and as waves - this is known as wave-particle duality
How does light act as a particle?
Light interacts with matter, such as electrons, as a particle - the evidence of this is provided by the photoelectric effect
How does light act as a wave?
Light propagates through space as a wave - the evidence for this comes from the diffraction and interference of light in Young’s Double Slit experiment - diffraction occurs when waves pass through a gap or around an obstacle and the waves spread out
What is the De Broglie wavelength?
The De Broglie wavelength is defined as the wavelength associated with a particle - this was based on the fact that of light can behave as a particle, then particles like electrons can behave like waves
What is the De Broglie equation?
λ = h/p
λ = De Broglie wavelength in m
h = 6.63x10^-34 Js
p = momentum in Ns
What are photons?
Photons are fundamental particles which make up all forms of EM radiation - they are massless particles which carry discrete amounts of energy (each photon carries a specific amount of energy and transfers this energy all in one go)
How do you calculate the energy of a photon?
E = hf or E = hc/λ
E = energy of a photon in J
h = 6.63x10^-34 Js
f = frequency in Hz
c = 3x10^8 ms^-1
λ = wavelength in m
How do you calculate the momentum of a photon?
Despite a photon having no mass, it still has momentum - p = E/c
p = momentum in Ns
E = energy in J
c = 3x10^8 ms^-1
What is an electronvolt?
An electronvolt is defined as the energy gained by an electron travelling through a potential difference of one volt - it is used to help express very small energies as quantum energies tend to be much smaller than 1J - 1eV = 1.6x10^-19 J
How do you convert between eV and J?
eV → J: multiply by 1.6 × 10-19 J
J → eV: divide by 1.6 × 10-19 J
What is the relation of an electronvolt to kinetic energy?
When a charged particle is accelerated through a potential difference, it gains kinetic energy - if an electron accelerates from rest, an electronvolt is equal to the kinetic energy gained:
eV = 1/2mv^2
What is the photoelectric effect?
The photoelectric effect is the phenomenon in which electrons are emitted from the surface of a metal upon the absorption of electromagnetic radiation - electrons removed from a metal in this way are called photoelectrons - this phenomenon shows that light is quantised (they can only certain magnitudes) as each electron can absorb only a single photon
What is the threshold frequency and wavelength?
- The threshold frequency is the minimum number of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal
- The threshold wavelength is the longest wavelength of incident electromagnetic radiation that would remove a photoelectron from the surface of a metal
These are properties of a material and vary from metal to metal
What is meant by the work function?
The work function or threshold energy of a material is defined as the minimum energy required to release a photoelectron from the surface of a material
What is meant by the stopping potential?
The potential difference required to stop photoelectron emission from occurring
What does the maximum kinetic energy of photons depend on?
The maximum kinetic energy of photons depends on the frequency of the incident photons and the work function of the metal - changing the intensity of the incident radiation does not alter anything as this only changes the number of photons incident on the plate and the number of photoelectrons emitted from the plate
How do you calculate the total energy of a photoelectron?
The threshold energy + the kinetic energy of the photoelectron - The energy within a photon is equal to hf - This energy is transferred to the electron to release it from a material (the work function) and gives the emitted photoelectron the remaining amount as kinetic energy
E = hf = Φ + 1/2mv^2 (EKmax)
Above energy hf0 = Φ, where f0 = threshold frequency, photoelectric emission can occur
