Another Look at the Atom

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, uncertainty principle

Models of the atom

• 1803 Dalton - tiny indestructible spheres • 1897 Thompson - plum pie model • 1911 Rutherford - planetary model with

electrons in random orbitals • 1913 Bohr - orbital model – Niels Bohr, a student of Rutherford, used the

information from earlier work to develop his model of the atom.

Bohr Model

Bohr believed that energy contained in electrons 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, ...)

Quantized electrons• 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– The electron is now back at its ground state or resting state

Heisenberg's Uncertainty Principle

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

Quantum Mechanical Model

1926 Erwin Schrodinger -• Erwin Schrodinger developed a new model

based on the quantum model of Bohr and the observations of Heisenberg. According to his calculations, electrons exist in cloud densities around the nucleus.