Atomic Model

Description

A styrofoam model is presented that incorporates the ideas of the ancient Greeks, Dalton, Bohr, Rutherford, and Schrodinger.

Procedure

Show the model, and discuss the historical evolution of the atomic model.
The ancient Greeks held the idea that atoms were discrete particles with hooks that permitted them to bind to one another. Dalton also held this kind of view.
The Thomson model consisted of dispersed positive and negative charges.
Rutherford suggested that all of the positive charge and nearly all of the atomic mass was concentrated in a small region called the nucleus. Bohr suggested that electrons surrounded the nucleus in fixed circular orbits.
Current models suggest that electron positions cannot be precisely specified. Instead, the electron is viewed in terms of the likelihood of its being in a particular region. The shapes of surfaces that would hold the electron for a large fraction of the time, say for 90% of the time, are called probability contours (orbitals).

Handout Makeup

Name _____________________________ Class _______

Teacher______________________________

DoChem 034 Atomic Model

Watch the movie. Describe the atomic models in the movie and relate them to the present theory of atomic structure.

Teachers Guide

Purpose

To illustrate a few historical models of the atom.

Materials

1 model prepared from a large diameter styrofoam sphere and 3 egg-shaped styrofoam pieces, all painted as indicated.
Need pipe cleaners for bonding connectors.

Lab Hints

The model must be constructed in advance.

Time

Time to prepare model: 2 hours

Presentation: 5 minutes

Hazards

No special hazards are known to be associated with this demonstration.

Precautions

Follow normal laboratory precautions.

Disposal

Save the model for use in future years.

Background

Although it was recognized that the atom contained charged particles, the first model imagined these to be distributed throughout the volume of the atom.
Rutherford's work led to the nuclear model for the atom, with the positive charge concentrated in a small region called the nucleus. Bohr's work imagined electrons to occupy well defined orbits around the nucleus.
Today's model forgoes the hope of pinpointing the position of the electron. Instead, regions of electron probability are established. The probability contours shown would be imagined to contain an electron for a particular fraction of the time, say 90%. The orbitals shown in the movie are 3 p-type orbitals.

Key Words