Bohr Model of the Atom - Overview and Examples

Bohr Model of the Atom s The Bohr Model has an atom consisting of a small, positively-charged nucleus orbited by negatively-charged electrons. Heres a closer look at the Bohr Model, which is sometimes called the Rutherford-Bohr Model. Overview of the Bohr Model Niels Bohr proposed the Bohr Model of the Atom in 1915. Because the Bohr Model is a modification of the earlier Rutherford Model, some people call Bohrs Model the Rutherford-Bohr Model. The modern model of the atom is based on quantum mechanics. The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen. The Bohr Model is a planetary model in which the negatively-charged electrons orbit a small, positively-charged nucleus similar to the planets orbiting the Sun (except that the orbits are not planar). The gravitational force of the solar system is mathematically akin to the Coulomb (electrical) force between the positively-charged nucleus and the negatively-charged electrons. Main Points of the Bohr Model Electrons orbit the nucleus in orbits that have a set size and energy.The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.Radiation is absorbed or emitted when an electron moves from one orbit to another. Bohr Model of Hydrogen The simplest example of the Bohr Model is for the hydrogen atom (Z 1) or for a hydrogen-like ion (Z 1), in which a negatively-charged electron orbits a small positively-charged nucleus. Electromagnetic energy will be absorbed or emitted if an electron moves from one orbit to another. Only certain electron orbits are permitted. The radius of the possible orbits increases as n2, where n is the principal quantum number. The 3 → 2 transition produces the first line of the Balmer series. For hydrogen (Z 1) this produces a photon having wavelength 656 nm (red light). Bohr Model for Heavier Atoms Heavier atoms contain more protons in the nucleus than the hydrogen atom. More electrons were required to cancel out the positive charge of all of these protons. Bohr believed each electron orbit could only hold a set number of electrons. Once the level was full, additional electrons would be bumped up to the next level. Thus, the Bohr model for heavier atoms described electron shells. The model explained some of the atomic properties of heavier atoms, which had never been reproduced before. For example, the shell model explained why atoms got smaller moving across a period (row) of the periodic table, even though they had more protons and electrons. It also explained why the noble gases were inert and why atoms on the left side of the periodic table attract electrons, while those on the right side lose them. However, the model assumed electrons in the shells didnt interact with each other and couldnt explain why electrons seemed to stack in an irregular manner. Problems with the Bohr Model It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit.The Bohr Model provides an incorrect value for the ground state orbital angular momentum.It makes poor predictions regarding the spectra of larger atoms.It does not predict the relative intensities of spectral lines.The Bohr Model does not explain fine structure and hyperfine structure in spectral lines.It does not explain the Zeeman Effect. Refinements and Improvements to the Bohr Model The most prominent refinement to the Bohr model was the Sommerfeld model, which is sometimes called the Bohr-Sommerfeld model. In this model, electrons travel in elliptical orbits around the nucleus rather than in circular orbits. The Sommerfeld model was better at explaining atomic spectral effects, such the Stark effect in spectral line splitting. However, the model couldnt accommodate the magnetic quantum number. Ultimately, the Bohr model and models based upon it were replaced Wolfgang Paulis model based on quantum mechanics in 1925. That model was improved to produce the modern model, introduced by Erwin Schrodinger in 1926. Today, the behavior of the hydrogen atom is explained using wave mechanics to describe atomic orbitals. Sources Lakhtakia, Akhlesh; Salpeter, Edwin E. (1996). Models and Modelers of Hydrogen. American Journal of Physics. 65 (9): 933. Bibcode:1997AmJPh..65..933L. doi:10.1119/1.18691Linus Carl Pauling (1970). Chapter 5-1.  General Chemistry  (3rd ed.). San Francisco: W.H. Freeman Co. ISBN 0-486-65622-5.Niels Bohr (1913). On the Constitution of Atoms and Molecules, Part I (PDF). Philosophical Magazine. 26 (151): 1–24. doi:10.1080/14786441308634955Niels Bohr (1914). The spectra of helium and hydrogen. Nature. 92 (2295): 231–232. doi:10.1038/092231d0

How to Make a Fruit Battery

How to Make a Fruit Battery If you have a piece of fruit, a couple of nails, and some wire, then you can generate enough electricity to turn on a light bulb. Making a fruit battery is fun, safe, and easy. What You Need To make the battery you will need: Citrus fruit (e.g., lemon, lime, orange, grapefruit)Copper nail, screw, or wire (about 2 in. or 5 cm long)Zinc nail or screw or galvanized nail (about 2 in. or 5 cm long)Small holiday light with 2 in. or 5 cm leads (enough wire to connect it to the nails) Make a Fruit Battery Heres how to make the battery: Set the fruit on a table and gently roll it around to soften it up. You want the juice to be flowing inside the fruit without breaking its skin. Alternatively, you can squeeze the fruit with your hands.Insert the zinc and copper nails into the fruit so that they are about 2 inches (5 centimeters) apart. Dont let them touch each other. Avoid puncturing through the end of the fruit.Remove enough insulation from the leads of the light (about 1 in. or 2.5 cm) so that you can wrap one lead around the zinc nail and the other lead around the copper nail. You can use electrical tape or alligator clips to keep the wire from falling off the nails.When you connect the second nail, the light will turn on. How a Lemon Battery Works Here are  the science and chemical reactions regarding a lemon battery (you can try making batteries from other fruits and from vegetables): The copper and zinc metals act as positive and negative battery terminals (cathodes and anodes).The zinc metal reacts with the acidic lemon juice (mostly from citric acid) to produce zinc ions (Zn2) and electrons (2 e-). The zinc ions go  into solution in the lemon juice while the electrons remain on the metal.The wires of the small light bulb are electrical conductors. When they are used to connect the copper and zinc, the electrons that have built upon the zinc flow into the wire. The flow of electrons is current or electricity. Its what powers small electronics or lights a light bulb.Eventually, the electrons make it to the copper. If the electrons didnt go any farther, theyd eventually build up so that there wouldnt be a potential difference between the zinc and the copper. If this happened, the flow of electricity would stop. However, that wont happen because the copper is in contact with the lemon.The electrons accumulating on the copper terminal react with hydrogen ions (H) floating free in the acidic juice to form hydrogen atoms. The hydrogen atoms bond to each other to form hydrogen gas. More Science Here are additional opportunities for research: Citrus fruits are acidic, which helps their juices to conduct electricity. What other fruits and vegetables might you try that would work as batteries?If you have a multimeter, you can measure the current produced by the battery. Compare the effectiveness of different types of fruit. See what happens as you change the distance between the nails.Do acidic fruits always work better? Measure the pH (acidity) of the fruit juice and compare that with the current through the wires or brightness of the light bulb.Compare the electricity generated by fruit with that of juices. Liquids you can test include orange juice, lemonade, and pickle brine.