Spectroscopy is a leading technique in studying internal constitution, structure, and isotope shift of atoms, ions, and molecules. Atoms and ions usually do emit light when exposed to high amounts of heat which makes such spectra lines visible under spectroscope, clearly showing differences between various energy levels present in an atom. The aim of the experiment was to document spectroscope design and how such can be used to observe visible spectra lines of gaseous atoms namely the noble gases and hydrogen. The methods used included using a helium discharge tube to calibrate the spectroscope in order to locate the spectra lines relative to the reference line. The results showed that Hydrogen had the lowest number of visible spectra lines while Xenon had the highest. This was attributed to the number of energy levels in these atoms.
Key words: spectra lines, spectroscopy, photon, energy levels Introduction Analytical atomic spectrometry consists of numerous techniques on distinct principles and characteristics. Spectroscopy primarily entails studying the internal constitution of atoms, ions, and molecules including the hyperfine structure and isotope shift. On the other hand, spectra chemistry entails determining wavelengths with high degree of accuracy due to the sharpness of the spectra frequencies emitted by free particles. Usually, all atoms and ions emit light when exposed to high temperatures thus when observed on a spectroscope, a series of colored lines characteristic of the differences between various energy levels are observed.
This practical report details an experiment in which a simple spectroscope is developed to observe spectra lines in atoms and thus provide basis for qualitative analysis. Materials A grafting film, source of light, spectrophotometer, prism or diffraction grafting, and elements (H, Ne, Kr, Ar, Xe, He) Methodology A cigar or a cake box of at least one inch in depth was fitted with slots, one inch deep and 1/4 inch wide, at each of the two facing ends. Slot A was narrowed to create a light entrance slit of the spectroscope. This was achieved through fastening to it two razor blades so that the distance between the sharp edges became less than 1 mm. Light rays emitted from the source and passing through the entrance slit at A were thus, diffracted by the grafting B at an angle of 30 degrees when observed from a normal incidence. Care was taken so that the grafting was only handles at the edges.
Light was allowed to pass unbent through the grafting and observed forming an image of the slit at point C. At this point C, a 2-inch rectangular hole was cut and small piece of graph paper was pasted. For the sake of reference, one line near the center was darkened. A helium discharge tube was used to calibrate the spectroscope in order to locate the spectra lines relative to the reference line. A table with columns for scale reading was made whereby the wavelength in Armstrong units and the color of the line were recorded.
For this experiment, hydrogen (H) and noble gaseous particles (Ne, Kr, Ar, Xe, He) were observed using the spectroscope. Discussion and Interpretation of Results The following are acceptable wavelengths for electromagnetic radiation when atoms are heated under high temperatures.
Violet (representative - 4100), limits
Blue (representative - 4700), limits
4240 - 4912
Green (representative - 4700), limits
Yellow (representative - 5800), limits
Orange (Representative - 6000), limits
Red (representative - 6500), limits
Infrared, greater than
The early discoveries provides platform for new developments and explanation of atomic spectra and wavelength standards. For instance, according to Bohr Theory of hydrogen atom, wavelengths of the hydrogen emission spectra lines can be correlated by using Rodberg's constant (1. 0968 x 107 m-1) and lower and upper quantum numbers. R- Rodberg's constant m- Lower quantum number; n = upper quantum number For the Hydrogen atom above, 4 spectra lines are observed; using a scale whereby n = 2 to 5 and m = 1 to 4; then Becomes 1/ = R (1/32 - 1/52) = R (1/9 - 1/25) = R (0. 07111) = 7. 799 X 105 m-1 = 1.
282 x 10-6 m = 1282 nm From the results, Xenon has the highest number of spectra lines, followed by Krypton, Argon, Neon, and helium in that order. Also, differences in wavelengths are also affected by the number of spectra lines or intensity of spectra lines in various color regions. Different color regions in the scale represent different wavelengths. The spectrum form a hot gas of an element consists of discrete wavelengths that are characteristic of the element. Bohr contributed to development of the modern quantum theory by incorporating Max Plank concept of quantum theory and Einstein's description of photon energy.
In essence, electrons move in circular orbits of a given radius around the nucleus under the influence of the Coulomb force between the negative electron and the positive nucleus (Shipman, Jerry and Todd 234). However, in an allowed orbit, the electron does not radiate energy since the atom is stable at these orbits. Classical electromagnetic theory predicts that an electron moving in circle is accelerated and must radiate electromagnetic energy continuously. It does so only when an electron makes a transition from one allowed orbit to another allowed orbit. In this experiment, the validity of Bohr Theory of hydrogen is shown by the four spectra lines (wavelengths) of the visible spectrum. Conclusion In conclusion, this experiment validated the Bohr Theory of hydrogen whereby four spectra lines as predicted by Bohr were observed.
With respect to intensity of wavelength or spectra lines, Xenon has the highest number of spectra lines, followed by Krypton, Argon, Neon, helium and hydrogen. Krypton thus has the highest wavelength. Works Cited Shipman, James, Wilson Jerry and Todd Aaron. An Introduction to Physical Science. Mason, OH: C engage Learning, 2012. Print..