1.2 Basic ideas about atoms - spectroscopy Flashcards
(30 cards)
what is the speed of light?
3x10^8m/s
what is the equation between speed of light, frequency and wavelength?
c = λf
what does this equation show?
that wavelength is inversely proportional to frequency
what is planck’s law? what do each of these represent?
E = hf
E = energy of a photon in Joules
h = 6.63x10^-34
f = frequency
how are frequency and wavelength related, use the equation to explain this
f α 1/λ
summarise how we use the electromagnetic spectrum for spectroscopy
spectroscopic excitations come about as a result of the movement of an electron(s) from lower to higher levels or vice versa. We can use these to work out the energy gaps between subshells and orbitals
what does absorption spectroscopy measure?
light energy absorbed by an atom causing an electron to move from a lower energy level to a higher one
what do the black lines represent in the absorption spectra?
light of some wavelengths has been absorbed
what do the wavelengths of the black lines in the absorption spectra correspond to?
the energy taken in by the atoms to promote electrons from lower to higher energy levels
what does emission spectroscopy measure?
measure the light emitted when the excited electron falls back to lower energy levels
why does an emission spectrum consist of a series of sharp lines?
because the energy levels are quantised (so only certain energy transitions are possible and certain frequencies are observed)
state briefly the difference between absorption and emission spectra.
In absorption spectra, energy is abrosbed from light causing electrons to move from a lower energy level to a higher one. It is seen as dark lines against a bright background.
In emission spectra, energy is emitted as electrons fall back from a higher energy level to a lower one. It is seen as coloured lines against a black background
define ‘convergence limit’
the point in the emission spectrum when the separate lines cannot be distinguished at n = ∞
what does the convergence limit correspond to?
the point at which the energy of an electron is no longer quantised
what happens at the convergence limit?
the nucleus has lost influence over the electron and therefore ionisation occurs
how do you work out the ionisation energy from the convergence limit?
frequency at the convergence limit
E=hf
how would you convert from J per atom to kJmol-3
energy J per atom x avogadros constant ÷1000
how would you get from nm to m?
x10^-9
how wouldyou get from nm to mm?
x10^-6
nm to cm?
x10^-7
what are the two different atomic emission spectrum of hydrogen?
The Lyman (UV) series and The Balmer (Visible Region) series
as the hydrogen electron falls down to a lower energy level what is emitted?
energy in the form of electromagnetic radiation
what is the ionisation energy of hydrogen in the Lyman series?
difference of n=1 and n=∞
Where do the electrons fall from in the Lyman series?
from higher levels to n=1 or ground state
