Lab 2- Emission Of Light From Hydrogen And Metal Ions Flashcards
How will the spectroscope be calibrated in the experiment?
It will be calibrated using the known wavelengths emitted by helium, and then the same spectroscope will be used to determine atomic hydrogen emission line positions. The principle quantum numbers and their corresponding energies will be determined and assigned to the hydrogen emission lines.
How will the value of the Rydberg constant be determined in the experiment?
It will be determined experimentally.
What is the general theory regarding electrons and their energy levels?
Electrons in an atom can only exist in certain allowed energy levels. Electrons in a ground state atom can be excited to a high-energy state by absorption of energy, for example, from a high-voltage discharge. When the electron returns to a lower-energy state, radiation in the form of light may be emitted. The energy emitted is quantized, and corresponds to discrete frequencies (which are proportional to energies) and corresponding to wavelengths in the spectrum. The emission spectrum then consists of discrete lines rather than a continuum in which light is emitted at all frequencies. Many such electronic transitions take place with emission of light in the visible region of wavelength 370-700nm; these transitions can be observed with relatively simple equipment and the human eye. It is also possible to examine changes in energy states of atoms and molecules which do not correspond to radiation in the visible region, but more elaborate instrumentation is required.
Why are we examining hydrogen in detail in this experiment?
Because it has a simple emission spectrum that has been well characterized. The wavelengths of light in the electromagnetic spectrum corresponding to changes in electronic states in hydrogen were described empirically by Rydberg according to the formula: 1/lambda: Rydberg’s Constant (1.097x10^7m^-1)x (1/lower quantum number-1/higher quantum number)
Do transitions to nl=1 correspond to the most stable energy level or the least stable energy level? Why is this the case?
Most stable energy level; this is because nl=1 characterizes the state closest to the positively charged nucleus, the energies associated with removal or return of an electron involving this level are the highest. In fact, emission of energy for a transition to nl=1 is found in the ultraviolet region for all values of nh. The name given to this series of transitions is the Lyman series.
What is the trend for energy and wavelength as nl becomes larger?
Energy becomes smaller and the wavelength becomes larger.
Why are we particularly interested in the transition to nl=2?
Because this series, the Balmer series, results in emissions in the visible region that can easily be studied with a Bunsen spectroscope.
What are the 3 series for hydrogen and the nl and region of spectrum assigned respectively?
Lyman-Balmer-Paschen. LBP
Lyman-1-Ultraviolet L1U
Balmer-2-Visible B2V
Paschen-3-Infrared P3I
Define the important things regarding a Spectroscope
When light emitted from a discharge tube is passed through a prism, it is refracted into components of different colors. Each of the lines in the spectrum thus produced is light of a particular wavelength. The spectroscope is an instrument containing a diffraction grating, a scale, and eyepiece for viewing the spectrum. DSE
Is it easy to manufacture a spectroscope containing a scale such that when light of 400nm is viewed through the eyepiece, it falls on a line on the scale marked 400nm?
No, it isn’t.
What is usually done for measurements in the spectroscope?
Approximate numbers are put on the scale.
How does one calibrate a spectroscope?
Using a high-voltage discharge tube containing gas that produces lines whose wavelengths are accurately known. The scale reading at which these lines appear correspond to known wavelengths. A calibration curve is then constructed by graphing the scale readings versus the known wavelengths . Along the x-axis are the scale readings, and along the y-axis are the known wavelengths.
What is the purpose of using a flame test in this experiment?
A high temperature flame (such as one from a Bunsen burner) can also be used to promote electrons in metal atoms to excited states. When the electrons return to the ground-state configuration, energy in the form of light of a wavelength (or color) characteristic of the element is emitted. This light appears to color the flame, thus the term flame test.
