cName: Nicholas Cassel
Gen Chem 1210
23 March 2013
Blinded By the Light
In this experiment we were provided a cereal box spectrometer to observe the emission lines of noble gases and hydrogen. Based on the scale readings on the spectrometer and the Balmer-Rydberg formula, their wavelengths and percent error were able to be extrapolated. Based on the literature values, the cereal box spectrometer proved its value as a decently accurate spectrometer.
Every element and subsequent atom associated emits light; also know as electromagnetic radiation, when in an excited state. Analyzing this emitted light can give insight to the makeup and characteristics of them. The light given off by an energetically excited atom is not a continuous distribution of all possible wavelengths, but rather consists of a few wavelengths giving a series of discrete lines. Spectroscopy is the analysis of that emitted light and its dispersion into to it’s component wavelengths and colors.
Niels Bohr explained the discrete spectrum of hydrogen
by relating it to the electron. Normally the electron in the hydrogen atom is located in the first energy-level. When a hydrogen atom atoms gains energy, the electron moves from a lower energy-level to one of higher energy. The energy gained by the atom is exactly the amount of energy needed to move the electron from the lower energy-level to the higher energy-level. With its electron in a higher energy-level, the atom is now in an unstable, higher energy, excited state. The tendency is for electrons to occupy the lowest level available. So shortly after gaining the energy, the electron returns to a lower energy-level. Energy must be given up when this occurs, and the energy is lost as light. Each line in the emitted light of hydrogen represents the movement of an electron from a specific outer level to a specific inner one.
We judge this emitted light against the electromagnetic spectrum with a spectrometer. A spectrometer is an instrument that gathers light particles (photons) and is able to determine the chemical make-up of the source. A spectrometer breaks up a beam of light into its component colors. Usually it uses a prism or a diffraction grating. Light goes in as a beam of white light and is split into a rainbow. Particular atoms generate light at particular frequencies (colors) and so can be identified in the lab. The electromagnetic spectrum is the range of all possible wavelengths of electromagnetic radiation. This range extends from sub-radio waves to gamma rays. Visible light falls within this spectrum. The light emitted by each element is independently different and has different “colors” that can be seen on the spectrum. The Balmer-Rydberg formula is used to describe the emission lines of hydrogen across the entire spectrum and not just visible light. The purpose of this laboratory experiment is to see the emitted wavelengths of elements through a spectroscope and calculate the wavelengths with the Balmer-Rydberg formula. Then with the calculations, relate them to the atom. I believe that with the correct calculations and comparisons the wavelengths, each emission line will be able to be determined.
The procedures as per the lab manual page 258 (Grossie, Underwood, 2012) were to first calibrate our spectroscope with helium. Looking at helium through the spectroscope, the emission lines where seen and recorded. That data was then put into Microsoft Excel and put into a graph. From the graph a formula was extrapolated. The spectroscope was used to observe and record the fours spectral lines of hydrogen. The calibration plot from helium determine the wavelengths of each of the lines by extrapolation. Comparing the calculated wavelengths to those determined from the calibration plot, and then calculate the percent error for the values. Then the spectroscope was used to view the spectral lines of argon, krypton, neon and Xenon. These...
References: Grossie, D. & Underwood K. (2011).Laboratory Guide for Chemistry. “Atomic Spectrometry”, Wright State University. Dayton, OH.
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