1 / 10

Atomic Spectra

Atomic Spectra. Rutherford Model - Atom is mostly empty space with all the positive charge concentrated in a tiny massive central core. He also suggested a planetary model where electrons orbit the nucleus. Although a major step forward, this model was flawed.

claudia-mcintyre
Download Presentation

Atomic Spectra

An Image/Link below is provided (as is) to download presentation 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. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Atomic Spectra • Rutherford Model - Atom is mostly empty space with all the positive charge concentrated in a tiny massive central core. He also suggested a planetary model where electrons orbit the nucleus. Although a major step forward, this model was flawed. • Heated solids, liquids and dense gases emit light with a continuous spectrum of wavelengths. Less dense gases emit a discrete spectrum (emitted light is due to individual atoms, not interactions between atoms).

  2. Emission Spectrum - when energy is transferred to atoms, the atoms absorb this energy and then emit it in the form of light. The spectrum of a gas is a series of lines of different colors, each line corresponding to a specific wavelength of light emitted from the atoms of the gas.

  3. Absorption Spectrum - a gas that is cool will absorb certain wavelengths of light that is shone on it. A spectrum will show dark lines where wavelengths have been absorbed. • Cool gaseous elements absorb the same wavelengths that they emit when excited. These spectra serve as a key to the structure of the atom.

  4. Bohr Model • Visible spectrum of hydrogen consists of four lines - red, green, blue, and violet. Rutherford model could not explain this, and also predicted an unstable atom. • In 1911, Niels Bohr attempted to unite Rutherford's nuclear model with Einstein's quantum theory. • Rutherford focused on the nucleus, Bohr focused on the electrons. • He suggested that the energy of an electron (and its radius) is quantized, and also that the laws of electromagnetism do not hold inside the atom!

  5. The electron can exist in different energy levels. Smallest energy level is the ground state. If an electron absorbs energy, it makes a transition to an excited state; however, it usually remains in this state for only a fraction of a second. • Light is only emitted when an electrons drops to a lower energy state. • The change in energy of an electron when a photon is absorbed or emitted is equal to the energy of the photon

  6. Bohr derived an equation for the energy of an electron in an atom • wheren is called the principal quantum number; (the radius increases with n2, the energy depends on 1/n2) • When changing energy levels, electrons can jump directly or in steps; for example, going from n=3 to n=1 state, electron can go from 3 to 1, or from 3 to 2 and then from 2 to 1.

  7. As a result, three different photons could be emitted in this example (each of whose energy is equal to or less than the energy that the electron originally absorbed) • Fluorescence – objects emit visible light after absorbing ultraviolet light (fluorescent lights) • Phosphorescence – electrons can be raised to metastable states; these states last much longer than higher energy levels in typical atoms (luminous watch dials)

  8. Quantum Model of the Atom • Bohr model calculated the emission spectrum and ionization energy of hydrogen atom, determined energy levels of the elements, and explained some of the chemical properties of the elements; however • His postulates could not be explained on the basis of known physics and only worked for hydrogen • de Broglie suggested that each electron in the atom is actually a standing wave. This implies that wave-particle duality is at the root of atomic structure

  9. Schrodinger and Heisenberg used de Broglie's wave model to begin a quantum theory of the atom. • Radius of the orbit of the electron not the same as the radius of planet around the sun, but is actually much harder to visualize. • Quantum model of the atom only predicts the probability that an electron is in a specific location. The region in which there is a high probability of finding the electron is called the electron cloud. • Philosophic Implications - probability (Quantum) vs determinism (Newtonian)

  10. Heisenberg Uncertainty Principle - position and momentum of a particle cannot both be precisely known at the same time • Quantum model predicts the same energy levels as Bohr for hydrogen. Bohr model only had one quantum number (principal); quantum model uses 4 quantum numbers (principal, orbital, magnetic, spin) • Quantum mechanics uses this model to predict many details about the structure of the atom -- it takes powerful computers to calculate accurate details for many atoms

More Related