Experiment 5 Post-Lab Quiz

what are the other goals of this experiment?

- calibrating a spectroscope with an Hg vapor lamp to create a calibration curve - analyzing the emission spectrum of both H and He - comparing alkali and alkaline earth spectra

what is the range of the visible spectrum?

400nm to 700nm

definition of spin state, singlet state, triplet state, ionized, orbital, grating, shielding, and the Zeff

- spin state is the direction of the electron that is either up or down - singlet state is when the electrons are antiparallel - triplet state is when electrons are parallel (both are in the same direction) - ionized is when atoms are charged by removing electrons (which requires energy) - an orbital is the location of the electron - grating is when light is separated into distinct wavelengths in order to diffract light - shielding is when there is more than one electron, causing more repulsion due to electron-electron interaction shielding also effectively reduces the pull of the nucleus on the electron - the Zeff is the effective nuclear charge and has to do with electron shielding and the charge experienced by an electron due to shielding Zeff is always less than the actual nuclear charge (Z), in which a greater value attracts electrons more and lowers the energy of the orbitals

how do we identify an unknown salt?

1. blank the sticks (in order to gather the background of the wood) 2. hold the salt under the fire using the sticks (to bring excited states to observe our emissions) 3. record the spectra (through grating on the spectroscope which separates the one color that we see into multiple wavelengths) 4. eliminate possibilities based on the absence of lines 5. account for EACH line

what angle do we clamp our bunsen burner at and why? why we do clamp at the base of the bunsen burner?

45º angle, so that the melting salts do not end up in the head of the bunsen burner, and we clamp at the base because it is the part that does not heat up and cannot melt the plastic prongs

why is Hg used to calibrate a spectroscope?

Hg is used because the emission wavelengths are precisely known and identifiable

how does a spectroscope work?

a spectroscope isolates a beam of light and passes it through a prism, which diffracts light in a process called grating, which is presented on a scale within the spectroscope that allows us to see the individual wavelengths of each sample light enters through a slip in the spectroscope, bounces off a prism-like structure called grating, which diffracts this light onto a scale in distinct wavelengths

how do you determine which transition will emit the smallest wavelength (i.e. the highest energy)?

choose the lowest nf and the highest ni

how does the electron spin affect the emission spectra?

depending on the electron spin, there will be different levels of energy helium has a triplet state as well as a singlet state, so depending on the different permutations of the electron spins, it increases the number of emission spectra that are observable so because helium has more electrons, resulting in more spins, it will increase the number of lines that we can see

what does each line on the emission spectrum represent?

each line is an emission event in which an electron transitions from a higher energy level to a lower energy level

what occurs at an emission and absorption?

emission occurs when an electron goes from a higher energy level to a lower energy level (for example, from n=6 to n=5), while absorption occurs when an electron goes from a lower energy level to a higher energy level, requiring energy to do so (for example, from n=5 to n=6)

why does helium have more lines than hydrogen?

helium overall has more electrons than hydrogen which is why more lines show up in the emission spectrum, because more electrons mean more electrons being excited, emitted more energy so that more lines show up

what is the relationship between energy, frequency, and wavelength?

higher energy means higher frequency, but a lower wavelength (for example, purple has a higher energy than red, a higher frequency than red, but a lower wavelength than red)

what is the difference between hydrogen and helium?

hydrogen and helium have different electron states, and due to the bohr model, electrons orbit the nucleus as fixed energy levels which is why we cannot apply the bohr model to helium, due to electron shielding (because helium has 2 electrons) this is also because each electron is attracted to the nucleus while also repulsive towards one another

what is the difference between hydrogen and helium emission spectra?

hydrogen only has one electron, which means that its energy level of an orbital is determined by n, but helium has two electrons which means that its energy level is determined by both n and l the difference in energy between sub-shells in multi-electron systems results from electron-electron repulsion because there are more electrons, the atoms repel each other, so the electron is less tightly-bound to the nucleus than it would be if the other electrons were not present, which causes different attraction to nucleus so our s and p orbitals no longer than the same energy an electron that transfers from the 1s to the 2s or 2p in hydrogen requires the same energy, but 2s and 2p are different in helium and requires different amount of energy, resulting in more possible transitions for a multi-electron atom

why do energy levels get closer together at higher levels?

if we look at the rydberg equation, we can see that we are dividing by a bigger number, which means that the distance between the orbitals decreases as the n-value increases, which is due to shielding and squaring the n-value this is also because, when electrons are closer to the nucleus, they require more energy to leave that level due to their attraction to the nucleus, so if they are further from the nucleus, there is less attraction which therefore requires less energy to move around

is 2p always higher than 2s?

no, it depends on the spin state and overall electron shielding

which spin state is at a higher energy?

singlet states are at a higher energy than triplet states because triplet states have unpaired electrons that are located at different orbitals and have a different spin

what is the balmer series and why do we use it over other series, such as the lyman series or the paschen series?

the balmer series is the emission spectrum for visible light (where nf = 2), and we use it over the lyman series (where nf =1) because the lyman is too big and corresponds with UV light instead, while the paschen series (where nf=3) is too small and corresponds with infrared light

bohr model and its limitations

the bohr model explains the atomic structure of a hydrogen atom, which a positively-charged nucleus at its center surrounded by electrons in different energy levels however, the bohr model does not work with larger atoms (such as helium due to its two electron) due to electron shielding and electron-electron repulsion the bohr model also cannot predict the intensities of spectral lines, nor can it predict the splitting of spectral lines in a magnetic field

how does the second electron affect our possible excited states?

the energy of an electron has different s and p orbitals, which allows us to have more excited states possible as well as more spin states possible, overall having more unique emissions possible

what is the purpose of wetting/blanking the sticks?

the wet sticks act as a baseline for our measurements, so when we burn the sticks, we can just subtract the spectrum that it emitted from when we burn our unknown material, as a way to isolate the spectrum of the unknown wetting the sticks also lessens the burning so that less light is emitted that could show up in our emission spectrum

what is the difference between ionized He and H?

their different number of protons means that the electron experiences a different pull by the nucleus (so if there are more protons, then the ONE electron would feel more attracted to it), so just because He+ and H have the same number of electrons doesn't mean can ignore protons as a factor as well

what is the pauli exclusion principle?

there are up to two electrons with paired spins per orbital

why doesn't the bohr model work for the first ionization energy of helium?

this is because of electron shielding since helium has two electrons and these two electrons are repulsive, so the bohr model can only be applied to one electron systems

when there is only one electron, there is no shielding, so why are the energy levels the same distance apart?

this is due to the distance from nucleus, as well as the squaring in the denominator, in which the distance decreases as the energy level increases

what is the main goal of this experiment?

use a spectroscope to characterize emission from hydrogen to helium (relative to Hg) and analyze an unknown mixture from multiple electron systems

what are the characteristics of a wave?

wavelength - the distance between corresponding points on adjacent waves, can be either crest to crest or trough to trough and is measured in meters amplitude - the size or height of a wave - measured from the middle of a wave to either the peak or the trough, looks at the brightness (intensity) frequency - the number of complete cycles of the wave passing through a point per second - in units of 1/s or Hz

how do we excite the elements that are being used?

we can excite the elements using either heat or an electrical current

how do we cause emissions to occur?

we need light energy for emissions, so we use a discharge tube in which the light source excites certain electrons so that energy is released and move from a higher energy level to a lower energy level

why does a triplet state have lower energy?

when electrons transition, they can move up and down energy levels with the same spin, but when two electrons that are parallel, one cannot move to the ground state with another parallel electron due to the pauli exclusion principle (which states that electrons have to be antiparallel if they occupy the same orbital), thus resulting in lower energy

could the emission spectrum of another element be used to calibrate the spectroscope?

yes, you can use any spectrum where the wavelengths are clearly identifiable lines