quantum phenomena Flashcards
what word describes the energy levels that electrons occupy?
discrete energy levels
what does discrete mean?
the energy levels that electrons occupy have a specific energy, it can’t vary from these values (like discrete data in maths)
what is the lowest possible energy state and electron can occupy?
ground state
what is the process by which an electron moves from a lower energy state to a higher energy state?
excitation
what is the process by which an electron moves from a high energy state to a lower energy state?
de-excitation
if a photon is able to excite an electron from one energy state to a higher energy state, what must be true about the photon?
the energy of the photon must be the same as the difference in energies of the 2 discrete energy levels it is moving between
when a electron de-excites to a lower energy level, what is emitted?
a photon is emitted, with the same energy as the difference between the 2 discrete energy levels
what is an electron volt?
a unit of energy
what is ionistaion?
when an electron gains sufficient energy to leave the atom all togther, forming a positively charged ion
list 4 ways an electron could become excited/ionisied
absorption of a photon
high voltage
collision with a free electron
high temperatures
in an exam question about emission/absorption spectra, what is the 1st thing you say?
electrons occupy discrete energy levels
explain how emission spectra form
electrons are excited to a higher energy level (e.g. because of high temperatures)
electrons de-excite from higher energy levels to lower levels
the electron release energy as a photon
the energy of the photon is equal to the difference in energy of the levels
energy is inversely proportional to wavelength
these wavelengths can be recorded and displayed as a discrete line on an emission spectrum
why do different elements produce different emission spectra?
different atoms have different (discrete) energy levels and a different number of electron, so the photons emitted have different (discrete) energies
explain how an absorption spectra is produced
electrons occupy discrete energy levels
when white light passes through a cooler gas, some frequencies of the white light are absorbed, and some pass through the gas.
this is because the electrons in the gas can only be excited by certain frequencies of light, as the photons must have the exact same energy as the differences in energy levels the electron is being excited between
the light reaching the detector is “missing” certain frequencies - there are dark lines where a given frequency has been absorbed by the gas.
explain how a fluorescent tube works
glass tube with a fluorescent inner coating (phosphor coating)
contains mercury vapor at a low pressure
when there is a high potential difference across the tube, atomic electrons are excited by the collision of free electron in the tube
when the mercury atoms de-excite, they emit ultraviolet photons.
the ultraviolet photons are absorbed by the atoms in the fluorescent coating and excite them.
coatings atoms then de-excite, releasing photons of av isible wavelength.
(more efficient than a filament lamp)
gold leaf electroscope: explain why the gold leaf rises up when light (of a given wavelength) is incident on the top plate
electroscope is given a negative charge, by passing a current through it
this causes the metal stem and gold leaf to repel each other
when the EM radiation is incident on the metal plate, electrons are released
the electrons being released from the metal plate cause the metal stem to become less negatively charged, meaning the gold leaf lowers and the repulsion between the stem and leaf reduces
define the photoelectric effect
electrons are emitted from a metal plate when UV light is incident on the plate. energy is transferred from the light
in the photoelectric effect: what happens if you increases the intensity of visible light?
nothing - frequency is too low for photoelectrons to be emitted
in the photoelectric effect: what happens when you increases the intensity of UV light?
rate of release of photoelectrons increases - more photons are incident on the surface, 1 photon interacts with 1 electron
in the photoelectric effect: what can be said about the time between turning the light on and the emission of electrons? what does this show?
photoelectric effect is instantaneous
in an exam question about the photoelectric effect, what is the first thing to state?
one photon interacts with one electron
define threshold frequency
the minimum frequency (and therefore energy) of light required to release electrons from the surface of a metal
what can be said about the speed of an electron emitted due to light, where the frequency of the light is equal tot he threshold frequency?
no “leftover” energy, so kinetic energy = 0J so speed = 0m/s
define work function
minimum amount of energy required to release photoelectrons from a metal surface
Φ = hf0
