So just remember, we'll keep the words "orbit" and "orbital", though we are now using them to describe not a flat orbital plane, but a region where an electron has a probability of being. Electrons are kept near the nucleus by the electric attraction between the nucleus and the electrons. Kept there in the same way that the nine planets stay near the Sun instead of roaming the galaxy.
Unlike the solar system, where all the planets' orbits are on the same plane, electrons orbits are more three-dimensional. Each energy level on an atom has a different shape. There are mathematical equations which will tell you the probability of the electron's location within that orbit. Let's consider the hydrogen atom, which we already drew a Bohr model of.
Probable locations of the electron in the ground state of the Hydrogen atom. What you're looking at in these pictures are graphs of the probability of the electron's location. The nucleus is at the center of each of these graphs, and where the graph is lightest is where the electron is most likely to lie. What you see here is sort of a cross section. That is, you have to imagine the picture rotated around the vertical axis. So the region inhabited by this electron looks like a disk , but it should actually be a sphere.
This graph is for an electron in its lowest possible energy state, or "ground state. Notice that at the center, where the nucleus is, the picture is dark, indicating that the electron is unlikely to be there. The two light regions, where the electron is most likely to be found, are really just one region.
Remember, you have to mentally rotate this around a vertical axis, so that in three dimensions the light region is really doughnut shaped. Molecules also produce spectral lines, but their spectra are much more complex than the spectra of single atoms, and typically show broad bands instead of narrow lines, as in Fig.
Examining different kinds of light with a spectroscope reveals a wide variety of spectra. The appearance of a spectrum tells us something about the physical conditions which produce the light.
For example, a continuous spectrum , like the one at the top of Fig. A hot solid, liquid, or very dense gas produces a continuous spectrum; while a wide range of wavelengths are always present, the overall color of the light depends on the temperature. For example, a bar of iron heated in a fire glows dull red; if heated more it glows orange, and if heated well beyond its melting point it shines with a brilliant blue-white light.
In contrast, an emission spectrum , like the one in the middle of Fig. Excited atoms have electrons in high orbits, and these emit photons with specific wavelengths when they jump back down to lower orbits as explained above. Finally, an absorption spectrum , like the spectrum of sunlight shown in the bottom of Fig. Absorption spectra are produced when light from a hot object travels through a cooler, dilute gas. When a photon with exactly the right wavelength encounters an atom of the cool gas, it is absorbed and its energy used to kick an electron into a higher orbit; if enough atoms of gas are present, all the photons of that wavelengths are absorbed, while photons with other wavelengths get through.
The atmospheres of stars produce absorption spectra. An element produces bright and dark lines with the same wavelengths. For example, hydrogen has three prominent lines with wavelengths of nm, nm, and nm; these appear dark if the hydrogen is absorbing light, and bright if it is emitting light, but the same three wavelengths are seen in either case.
In some situations, we find spectra which mix different kinds of features: for example, a continuous spectrum with bright emission lines superimposed. Some stars, as they age, produce continuous spectra with dark absorption lines and bright emission lines; this is usually a sign that the star is ejecting gas in a stellar wind.
In the lab, we will explain how to use spectroscope, and how to adjust it so you can measure wavelengths accurately. You will then have a chance to view different types of spectra.
We will set up several different discharge tubes, in which various elements are excited electrically. You will be asked to identify these elements by looking at the light they produce using your spectroscope.
Every gas shines with its own special colors of light. These colors are like a fingerprint because no two gases give off exactly the same colors. Streetlights filled with sodium gas give off a dark yellow light.
Only sodium atoms give off that particular shade of yellow. Orange neon signs are filled with pure neon gas. Other colors of neon signs are actually neon mixed with other types of gases, like helium or argon. The unique colors of light produced by a gas are called its " spectrum ".
Question a7afe. Question fb. Why is the electromagnetic spectrum continuous? Why is the electromagnetic spectrum a transverse wave? Why are atomic spectra of an element discontinuous? Why is the electromagnetic spectrum important?
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