 Another Look at the Atoms:

Objectives:

1.    Distinguish between a continuous spectrum and a line spectrum.

2.    State the main idea in Bohr's model of the atom.

Key Terms:

line spectrum    quantum number    ground state    excited state    matter wave    uncertainty principle

Web Resources:

Notes:

Line Spectrum.

As we stated in the last lesson, atoms can only absorb energy in quantized packets according to plank's constant.  As that quantized packet of energy is released by the atom a photon is created. The photon contains the exact quantum of energy absorbed by the atom The frequency of the emitted light is determined by the quantum

This single frequency of light is called a line spectrum.  More specifically, a line spectrum contains only certain frequencies of light which can be seen by passing the emitted light through a prism.  Look at the example below. (alta1.middlebury.edu)

Niels Bohr used the information in the line spectrum to develop his model of the atom. (www.cbu.edu/~mcondren/ bohr.gif)

Bohr believed that energy must be quantized to get to different energy orbitals around the atom.  He called the energy levels quantums. Each different quantum level is characterized by the letter n (n=1, n=2, n=3, ...) As an electron is quantized it jumps to the next energy level.  With sodium above, the outer (valence) electron jumps from n=3 to n=4. When the electron jumps it is considered to be in its exited state. When in its excited state the electron is farther from the nucleus than is normal. When the excited electron falls back to its normal quantum level a photon is released.

Heisenberg's Uncertainty Principle:

Bohr's planetary model came under some uncertainty and much scrutiny.  Heisenberg displayed that is is impossible to know where an electron is at any one particular point.  You can only be relatively sure where it is not.