Excited Elements Introduction •As electrons absorb energy they become excited and move to higher energy levels. •This energy is released in set amounts of energy (quanta) as the electrons fall back into lower energy levels. •This energy is released in many regions of the electromagnetic spectrum, including the visible region that you can see. •Quanta of light energy is called photons. In this lab, gases under low pressure receive electrical energy to excite the electrons. The electrons give off light in unique wavelengths and frequencies. The emitted light is passed through a spectroscope, which breaks light into its bright line emission spectrum. Each element produces a unique bright-line spectrum because each has a different number of electrons. The lines produced depends on the electron transition in that particular atom. When a solid is heated until it glows, it produces a continuous spectrum instead of a line spectrum. Spectroscopy is a valuable tool identify elements in samples. The composition of stars and other objects in outer space is determined using this technique. Helium was discovered as one of the elements in the sun before finding it here on Earth. Purpose: • To observe the characteristic bright line emission spectra produced by different elements. • Identify unknown samples by comparing unknown bright line spectrums to those that are known. Equipment/Materials: •High voltage power supplies •Diffraction grating glasses •Spectroscopes •Colored pencils •40 watt incandescent bulb/socket •40 watt fluorescent bulb/socket •Thermal Mitt •Spectral Tubes : Hydrogen, Helium, Neon, Mercury, Nitrogen, any other samples, and one unknown gas. Use white box for reflection; easier to read numbers on spectroscope! Safety: •DO NOT TOUCH the spectrum-tube power supply or spectrum tubes. Several thousand volts exist at the power supply and spectrum tubes are delicate. Procedure Obtain a spectroscope and look through it at an incandescent light bulb. The spectrum should appear when the slit in the spectroscope is pointed towards the bulb, just off center. Practice moving the spectroscope until you see a bright, clear image. Observe the color given off by the gas in the spectrum tube. Next, put on the diffraction grating glasses and observe the bright line spectra tube. Next, use a spectroscope and adjust it until the brightest image is oriented on your scale. Record the five brightest lines using the corresponding colored pencil and mark the line at the wavelength where it appears in the spectroscope. Repeat this for all known samples and the unknown sample. Observe and record the bright line spectrum for the fluoresent light. Observe and record the bright line spectrum for the incandecent light. This is how AUSIM packs the spectra tubes!
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