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Chemistry chapter 5 Electrons In Atoms--- Study Guide Atomic Models Thomson Model: discovered the e-; pictured e- embedded in a sphere of +ve electrical charges. Rutherford Model: most of an atom’s mass is concentrated in a small, positively charged region (nucleus) Bohr Model: Bohr proposed that an e- travel is found only in specific circular paths (orbits) around the nucleus— planetary model; o e- in a particular path have a fixed energy o EL of an e- is the region around nucleus where the e- is likely to be moving (like rungs of ladder); o an e- can jump from one EL to another; must gain or lose just the right amt of energy o A quantum of energy: amt of energy required to move an e- from its present EL to the next higher one. o In general, higher an e-, the farther it is from nucleus (more energy to resist the nuclear attraction). Quantum mechanical model: modern atomic theory describes the electronic structure of the atom as the probability of finding e- within a certain regions of space (atomic orbitals) o Designates EL of e- by means of principal quantum # (n) o Each # represents a principal energy level in an atom o n = 1, 2, 3, 4, 5, 6, 7 … ; increasing energy o distance of e- from nucleus increases with increasing value of n. o within each principal EL, e- occupy energy sublevels (orbitals) o each energy sublevel corresponds to an orbital of different shape, which describe where the e- is likely to be found. o s orbitals (spherical); p orbitals ( dumbbell-shaped; 3 different orientations in space); d orbitals (clover-leaf shapes …; 5); f (complicated; 7) o table 5.1 on page 131 Electron Configuration ways in which e- are arranged around the nuclei of atoms; 3 rules: Aufbau principle: o e- enter orbitals of lowest energy level first Pauli exclusion principle: an atomic orbital may describe at most two e-; to occupy the same orbital, 2 e- must have opposite spins (↑ or ↓) Hund’s rule: when e- occupy orbitals of equal energy, one e- enters each orbital until all the orbitals contain on e- with parallel spins ↑ ↑ ↑ ↑ ↑↓ ↑ ↑ ↑↓ ↑↓