Maria Goeppert-Mayer & the Nuclear Shell Model

Instructor: Betsy Chesnutt

Betsy has a Ph.D. in biomedical engineering from the University of Memphis, M.S. from the University of Virginia, and B.S. from Mississippi State University. She has over 10 years of experience developing STEM curriculum and teaching physics, engineering, and biology.

A German-American scientist named Maria Goeppert-Mayer developed a new model of the atomic nucleus that explained why some isotopes were more stable than others. In this lesson, learn more about her life and the nuclear shell model that she discovered.

Nuclei and Isotopes

Imagine for a minute that you were really small, so small that you could see into a single atom. What would you find in there? For a long time, scientists thought that the atom was the smallest particle that existed, but they were wrong. Inside each atom are even smaller particles!

In the center of each atom is a structure called a nucleus that contains two types of particles, protons and neutrons, that are tightly bound to each other.

  • Protons are always positively charged
  • Neutrons are neutrally charged
  • Together they are called nucleons, because they are always in the nucleus.

Outside the nucleus, there are tiny negatively charged particles called electrons.

In an atom, protons and neutrons are in the nucleus, while electrons are outside the nucleus
structure of an atom

Two elements are different from each other because they have a different numbers of protons. For example, an atom of hydrogen always has exactly 1 proton, while an atom of carbon always has exactly 6 protons.

However, atoms of the SAME element can have different numbers of neutrons. Sometimes a carbon atom has 6 protons but 8 neutrons! Either way, it's still carbon. Atoms of the same element that have different numbers of neutrons are called isotopes.

Although it seems like an atom could have any number of neutrons, that's not really what happens. Some isotopes are much more stable than others and, therefore, more likely to exist. Why does this happen?

A scientist named Maria Goeppert-Mayer wondered that too back in the 1940's, and she was determined to find out what was going on. What she discovered would totally change the way scientists understood atomic nuclei!

Who Was Maria Goeppert-Mayer?

Maria Goeppert (the name Mayer was added later) was born in Germany in 1906. Members of her family had been professors, scholars, and scientists for six generations before she was born, and her father always encouraged her to get an education and pursue her dreams.

She graduated from high school a year early and enrolled at the University of Gottingen. Although she was originally studying mathematics, she fell in love with physics and decided to pursue a Ph.D.

Maria Goeppert-Mayer (1906-1972) was a German-American scientist who developed the nuclear shell model of atomic nuclei
Maria Goeppert-Mayer

Goeppert got her Ph.D. in physics in 1930 and married an American chemist named Joseph Mayer the same year (adding the name Mayer). He was soon hired as a professor at Johns Hopkins, and Goeppert-Mayer followed him to America.

For many years, it was quite difficult for her to continue her own research. She was not allowed to work as a professor at the universities where her husband worked, but she managed to keep going anyway. She worked for free or for very little pay, and traveled back to Germany in the summers to continue her research at the University of Gottingen.

With the outbreak of World War II, things changed for Goeppert-Mayer. She was hired to work part time on the Manhattan Project, in which a group of scientists in America were working to build the world's first atomic weapon. After the war, she was able to continue working at the newly opened Argonne National Laboratory in Chicago. By that time, her husband was also working at the University of Chicago.

The Nuclear Shell Model

During her time in Chicago in the late 1940's, Goeppert-Mayer began to study isotopes and try to find out why some were more likely to occur than others. She found that there were certain special numbers of protons and neutrons that were always more stable. She took all this data and came up with a new model of the atomic nucleus that we call the nuclear shell model.

Before Goeppert-Mayer began studying atomic nuclei, scientists already knew that certain numbers of electrons were more stable also. This occurs because electrons are located in specific orbits, often called energy shells, that are associated with different amounts of energy.

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