Chemistry - A Molecular Science

Chapter 2 Quantum Theory

The electron configuration of an atom indicates the electron population of the filled sublevels. It is determined by three rules: •

Electrons seek the lowest energy orbital.

(^) •
No two electrons can have the same set of quantum numbers (Pauli exclusion principle).
(^) •
Electrons in sublevels that are half-filled or
less than half-filled remain unpaired and have the
same spin (Hund’s rule).
As a result of all of the above restrictions, the electron configurations of the atoms show the same periodicity as the periodic table. Fo
r the main group elements, the highest energy
electron is in an s sublevel (Groups 1A and 2A) or a
p sublevel (Groups 3A - 8A). The row
or period of the main group element corresponds
to the n quantum number of its highest
energy electron. The highest energy orbitals fo
r the transition elements lie in a d sublevel,
with an n quantum number equal to its period minus one.
After studying the material presented in this chapter, you should be able to: 1. explain the relationships between wavelength, frequency, and energy (Section 2.1); 2. define the term ‘quantized’ and use it describe line spectra and color (Section 2.2); 3. explain Bohr’s model of t
he atom and relate it to the
atomic spectrum of hydrogen
(Section 2.3);

4. explain how and why the electron

is treated like a wave (Section 2.4);

5. distinguish between acceptable and un

acceptable sets of quantum numbers (Section

2.5);

6. draw pictures of ns, np, and nd orbitals an

d describe their key features (Section 2.6); and

7.

write electron configurations for atoms based on their position in the periodic table (Section 2.8).

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