CHALLENGE ACTIVITIES
1. The activities presented in this class period highlighted the contributions of
several historically important individuals, but many more scientists and theorists have
contributed to the development of contemporary atomic theory. To expand on the
historical development of atomic theory, research the contributions of one or more
of the following individuals. After conducting your research, write a brief essay (2-3
paragraphs) that details (1) what the scientist discovered, (2) the experiment that the
scientist used to make that discovery, and (3) any other relevant information about
that scientist. Feel free to supplement your writing with diagrams, drawings, and/or
graphs.
Topic
Contributor(s)
Atomism
Leucippus
Nucleus of the atom
Hans Geiger, Ernest Marsden
Discovery of neutrons
Irene Joliot-Curie, James Chadwick
Isotopes
F.W. Aston
Atomic number
Henry Moseley
Electrons as particles and waves
Louis de Broglie
The nature of light
Christian Huygens (1629–1695), Augustin
Fresnel, Thomas Young (1883–1829), A.H.
Compton, Albert Einstein, Johann Jacob
Balmer
2. Almost all of the mass of an atom is located in the nucleus, with a very small
contribution from the electron cloud. The diameter of the nucleus is in the range of
1.75 fm (fm = femtometers, 1.75 x 10-15 m) for hydrogen, which is the approximate
diameter of a single proton. The atomic radius of a hydrogen atom (including its
electron cloud) is about 53 pm (pm = picometers, 5.3 x 10-11 m). Suppose the tennis
ball at this station represents the nucleus of a hydrogen atom. How large would the
atomic radius of a hydrogen atom be if its nucleus were the size of this tennis ball?