1.2 Basic ideas about atoms - spectroscopy Flashcards
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
why are the gaps between energy levels decreasing in absorption spectroscopy?
the energy differences is decreasing as frequency increases
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)
define ‘convergence limit’
the point in the emission spectrum when the separate lines cannot be distinguished at n = ∞
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
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
Where do the electrons fall from in the Balmer series?
from high energy levels to n=2
Why do the lines show up in the mroe energetic UV part of the spectrum in the Lyman series?
n=1 is closest to the nucleus (lowest energy) so far more energy is released when it returns to n=1
Why do we see the emitted energy as a line in the spectrum in the Balmer series?
they are in the visible spectrum
In the Balmer series, where does the electron fall from when it emits a red line? Green line? Blue line? Purple line?
Red falls from n=3 to n=2
Green falls from n=4 to n=2
Blue falls from n=5 to n=2
Purple falls from n=6 to n=2
Explain why hydrogen atoms emit only certain definite frequencies of visible light.
The electrons fall from higher energy levels to lower energy levels so the difference between the energy levels is quantised/fixed
