http://www.ck12.org Chapter 4. Atomic Structure
Rutherford’s model proved to be an important step toward a full understanding of the atom. However, it did not
completely address the nature of the electrons and the way in which they occupied the vast space around the nucleus.
It was not until some years later that a more complete understanding of the electron was achieved. This proved to be
the key to understanding the chemical properties of elements.
Watch a simulation of Rutherford’s experiment through The Concord Consortium’s Molecular Workbench. You will
need to download the Molecular Workbench application from http://mw.concord.org/modeler/index.html. After
installing Molecular Workbench, open it. You will see a browser window. In the address bar, type: "http://mw2.c
oncord.org/public/student/motionandforce/rutherford.cml ." You will be taken to the simulation.
Lesson Summary
- The three fundamental subatomic particles are the electron, the proton, and the neutron.
- Thomson used the cathode ray tube to discover the electron and determine its negative charge.
- Millikan determined the charge and mass of the electron with the oil-drop experiment.
- Rutherford’s gold foil experiment provided evidence for the atomic nucleus, a small dense core of the atom
which contains the positive charge and most of the mass. - The nuclear model of the atom is one in which the nucleus is composed of protons and neutrons, while
electrons are distributed throughout the rest of the space.
Lesson Review Questions
Recall
- What evidence did Thomson have for each statement below?
a. Electrons are negatively charged.
b. Electrons are identical and are present in all atoms. - What additional knowledge about electrons did Millikan’s experiment provide?
- Compare the mass (in amu) and relative charge of a neutron to that of a proton.
- What evidence did Rutherford have for each statement below?
a. Atoms are mostly empty space.
b. The nucleus of the atom is positively charged.
Apply Concepts
- Trace the development of the atomic model from Dalton to Thomson to Rutherford. Explain what experimen-
tal findings led each scientist to alter the previous model and how his new model fit with the new evidence.
Think Critically
- A hydrogen nucleus, which contains only a single proton, has a diameter of 3.7× 10 −^10 cm. The equation for
the volume of a sphere is^43 πr^3 , whereris the radius of the sphere.
a. Assuming that the nucleus is spherical, calculate its volume in cm^3.
b. Calculate the density of the hydrogen nucleus in g/cm^3.