What is atomic spectra?. In general The light which atoms give off is made up of specific wavelengths, called lines; observed by a spectroscope, the lines are, collectively, atomic spectra. In Bohrs experiment Transitions between the same energy levels always produce the same colour photon
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
What is atomic spectra? In general The light which atoms give off is made up of specific wavelengths, called lines; observed by a spectroscope, the lines are, collectively, atomic spectra. In Bohrs experiment Transitions between the same energy levels always produce the same colour photon Each time the electron jumps down a level it produces a photon, and the same jumps produce the same colours. Those same colour photons are the only ones that will bump the electron up to higher levels. Photons of other frequency will pass right through the atom. When you have a whole lot of atoms, you get all these different lines appearing at once and that's what scientists mean by the atomic spectrum. We talk about visible light because it's the easiest to experiment with, but we should talk about the "frequency" or "wavelength" of the photons, not their colour http://www.colorado.edu/physics/2000/quantumzone/lines2.html
In an atom, electrons have specific and discrete energies. There are many more energy states (or levels) in each atom than there are electrons. When an electron transitions (‘jumps’) from one energy level to another, it emits (if going from a higher level to a lower one) or absorbs (vice versa) light – a photon – with a discrete, specific wavelength. In any given set of conditions (pressure, temperature, magnetic field strength, etc), the collection of all those specific wavelengths is the spectrum of the atom … so atomic spectra are the spectra of atoms! • ‘atomic spectra’ refers to the line spectrum of ions too • Some of the visible lines of neon: l nm Colour540.1 green 585.2 yellow 588.2 yellow 603.0 orange 607.4 orange 616.4 orange 621.7 red-orange 626.6 red-orange 633.4 red 638.3 red 640.2 red 650.6 red 659.9 red 692.9 red 703.2 red
How do they emit light? • The glow of neon’s and fluorescents is nothing more glamorous than a bit of gas and a jolt of electricity. Sealed within the glass tubing of, say, an illuminated signboard (eg. Lights at BK) is a mixture of gases, one of which will always be neon. Left to itself, neon remains still and colourless. It is only when a current of electricity is passed through the gas that it reveals its garish talents. • When such an electrical change is applied, it stimulates electrons circling a neon atom’s nucleus. Though the suddenly excited electrons lack sufficient energy to elevate their orbits and move farther away from the nucleus. This condition lasts only an instant. Almost immediately, the electrons return to their unexcited state, emitting a burst of energy that is visible, as a brilliant orange-red application of a coating of phosphor powder to the inside of the tube will yield commensurate changes in colour. • Common fluorescent lights found in homes and offices work on a very similar principle. Within the glass tube is not neon but argon and mercury vapor. An electric current introduced into the mixture makes the gases give off faint bluish light and invisible ultraviolet radiation. These emissions would be useless as a light source were it not, again, for a phosphor powder coating on the inside of the tube. This substance reacts with the wavelengths created by the gases and shifts them into the visible spectrum. So efficient is the process that a 40-watt fluorescent lamp can yield as much light as a 150-watt incandescent bulb. But it is not efficiency that makes these lighting systems so appealing. It is, instead, their endless range of hues – from soft room lighting to glinting crimsons – that earns such simple atomic reactions such universal attention. • Invisible worlds clip:http://www.youtube.com/watch?v=0OZFrQOEyUs&feature=related