Electronic Structure of Atoms

Quantum Theory

1. Atoms and molecules can only exist in certain states characterized by definite amounts of energy. When an atom or molecule changes its state, it absorbs or emits an amount of energy (electromagnetic radiation) just sufficient to bring it to another state.

Electronic energy

2. When atoms or molecules absorb or emit light in moving from one energy state to another, the wavelength of the light is related to the energies of the two states by the equation

Efinal - Einitial = hc/l

3. The allowed energy states of atoms and molecules can be described by sets of numbers called quantum numbers

Relation between Energy difference, DE, and wavelength.

h = 6.626 x 10-34 J . s/ particle

c = 2.998 x 108 m/s

DE is in J/particle when wavelength is in meters

Ordinarily: DE is in kJ/mol, and wavelength is in nm

1 mole = 6.02 x 1023 particles
1 kJ = 103 J
1 nm = 10-9 m

Relation between wavelength and frequency:

For example:

Blue light, at a wavelength of 450 nm, has a higher frequency than red light with a wavelength of 650 nm.

The Atomic Spectrum of Hydrogen and the Bohr Model

1911--Niels Bohr, Danish physicist

spectroscope--instrument that breaks up light into its component colors

Hydrogen most studied because it is the simplest with only 1 e-

3 Points to keep in mind:

Quantum Mechanical Atom

Wave Nature of the Electron:

Send comments or questions to:
Gwen Sibert
Roanoke Valley Governor's School