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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
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