2.2 Energy Levels in Atoms Flashcards
what is the electron volt defined as?
the kinetic energy carried by an electron after it has been accelerated from rest through a potential difference of 1 volt
how do you convert between eV and J?
1 eV = 1.6 x 10^-19 J
what is the ground state?
the lowest energy level an electron can be in
how do electrons exist within an atom?
in certain well-defined energy levels, with each level having a number (e.g. n=1)
how do electrons move down an energy level?
by emitting a photon
are the energies of the photons emitted when electrons move down an energy level the same?
they are the same as these transitions are only between definite energy levels
what is the energy carried by a photon emitted after a transition equal to?
the difference in energies between the two levels of the transition
what is excitation?
electrons moving up an energy level by absorbing a photon with the exact energy difference/an electron with more than the energy difference
what is the equation for the energy from the transition between two energy levels?
delta E (change in energy) = E1 - E2
or: hf = E1 - E2
what is ionisation?
removing an electron from an atom
what is ionisation energy?
the amount of energy needed to remove an electron from the ground state atom
how do fluorescent tubes use the excitation of electrons?
- they contain mercury vapour, across which a high voltage is applied
- this high voltage accelerates fast-moving electrons that ionise some of the mercury atoms, producing more free electrons
- when this flow of free electrons collides with the electrons in the mercury atoms, the atomic mercury electrons are excited to a higher energy level
- when these excited electrons return to their ground states, they loose energy by emitting high-energy photons in the UV range
- a phosphor coating on the inside of the tube absorbs these photons, exciting its electrons to much higher energy levels
- these electrons then loose energy by emitting many lower energy photons of visible light
what happens if you split the light from a fluorescent tube with a prism/diffraction grating?
you get a line spectrum
how do prisms and diffraction gratings work?
by diffracting light of different wavelengths at different angles
what is a line emission spectrum?
a series of bright lines against a black background where each line corresponds to a particular wavelength of light emitted by the source
how do line spectra provide evidence that the electrons in atoms exist in discrete energy levels?
atoms can only emit photons with energies equal to the difference between two energy levels, so you only see the corresponding wavelengths in the line spectrum
what things emit continuous spectra?
hot things emit continuous spectra in the visible and infrared
how do continuous spectra form?
electrons are not confined to energy levels in the object, so every wavelength is emitted
when do you get a line absorption spectrum?
- when light with a continuous spectrum of energy passes through a cool gas at low temperatures, most of the electrons in the gas atoms will be in their ground states.
- photons of the correct wavelength are absorbed by the electrons to excite them to higher energy levels.
- these wavelengths are then missing from the continuous spectrum when it comes out of the other side of the gas
what is the relationship between the absorption and emission spectra of the same gas?
the black lines in the absorption spectrum match the bright lines in the emission spectrum
