Electrons

and the Bohr Model

Neils Bohr

• Neils Bohr was convinced that the atom could be pictured as a small positive nucleus with electrons orbiting around it as the planets orbit the sun.

The Bohr Model

• Neils Bohr pictured the electron moving in circular orbits corresponding to the various allowed energy levels.

Bohr proved incorrect

• • • Although the Bohr model paved the way for later theories, it is important to realize that the current theory of atomic structure is not the same as the Bohr model. Electrons do NOT move around the nucleus in circular orbits like planets orbiting the sun.

Bohr’s model is useful (in the chemistry classroom) for picturing the electrons present in an atom.

The Bohr Model – in use

• • • The Bohr model does NOT focus on the nucleus, but rather on the electrons.

The electrons are first placed on the innermost electron shell or energy level. Two electrons can fit in this level.

The Bohr Model – in use (cont.)

• The electrons are then placed on the second electron shell or energy level.

• • Eight electrons can fit in this level.

The electrons are then placed on the third electron shell or • energy level. 18 electrons can fit in this level.

The Bohr Model – in use (cont.)

• • • Electrons are represented by dots.

Electrons are usually placed singly at first and then doubly.

Example: Sodium

Let’s try one…

• Example: Sulfur