The excited atom can then emit energy only in certain (quantized) amounts as its electrons jump back to lower energy orbits Bohr's model also explained many important properties of the photoelectric effect described by Albert Einstein.Īccording to the Bohr model, when an electron is excited by energy it jumps from its ground state to an excited state (i.e., a higher energy orbital). The electron quantum leaps between orbits proposed by the Bohr model accounted for Plank's observations that atoms emit or absorb electromagnetic radiation only in certain units called quanta. Atoms give up excess internal energy by giving off photons as electrons return to lower energy (inner) orbits. Of all the photons (quantum packets of light energy) that an atom can absorb, only those having an energy equal to the energy difference between allowed electron orbits will be absorbed. Atoms may acquire energy that excites electrons by random thermal collisions, collisions with subatomic particles, or by absorbing a photon. Atoms with electrons in their lowest energy orbits are in a "ground" state, and those with electrons jumped to higher energy orbits are in an "excited" state. Subshells or suborbitals (designated s,p,d, and f) with differing shapes and orientations allow each element a unique electron configuration.Īs electrons move farther away from the nucleus, they gain potential energy and become less stable. The first shell can hold up to two electrons, the second shell (n=2) up to eight electrons, and the third shell (n=3) up to 18 electrons. Increasing numbers of electrons can fit into these orbital shells according to the formula 2n 2. The orbital shells are not spaced at equal distances from the nucleus, and the radius of each shell increases rapidly as the square of n. Additional orbital shells are assigned values n=2, n=3, n=4, etc. This first orbital forms a shell around the nucleus and is assigned a principal quantum number (n) of n=1. In the Bohr model, the most stable, lowest energy level is found in the innermost orbit. To account for the observed properties of hydrogen, Bohr proposed that electrons existed only in certain orbits and that, instead of traveling between orbits, electrons made instantaneous quantum leaps or jumps between allowed orbits. In addition, physicist James Clark Maxwell's influential studies on electromagnetic radiation ( light) predicted that an electron orbiting around the nucleus according to Newton's laws would continuously lose energy and eventually fall into the nucleus. Spectroscopic experiments, however, showed that hydrogen atoms produced only certain colors when heated. This predicted that when, for example, a hydrogen atom was heated, it should produce a continuous spectrum of colors as it cooled because its electron, moved away from the nucleus by the heat energy, would gradually give up that energy as it spiraled back closer to the nucleus. The classical model of the atom allowed electrons to orbit at any distance from the nucleus. Before Bohr, the classical model of the atom was similar to the Copernican model of the solar system where, just as planets orbit the Sun, electrically negative electrons moved in orbits about a relatively massive, positively charged nucleus.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |