Niels Bohr: Biography, Atomic Theory & Discovery

Instructor: Betsy Chesnutt

Betsy teaches college physics, biology, and engineering and has a Ph.D. in Biomedical Engineering

Niels Bohr was a Danish physicist who developed a model of the atom that we still use today to understand chemical bonding of atoms. In this lesson, learn about his life and the development of the Bohr model of the atom.

Niels Bohr: Early Life and Education

You probably know that all matter is made up of really, really tiny particles called atoms, but have you ever wondered exactly how an atom works and what the inside of one looks like? About a hundred years ago, a young Danish scientist named Niels Bohr wondered the same thing. His curiosity and research would lead him to develop a new model of the atom, known today as the Bohr model. But before we learn more about his work and achievements, let's get to know Niels Bohr.

In October of 1885 in Copenhagen, Denmark, Christian and Ellen Bohr welcomed a new baby boy to their family and named him Niels. He already had one older sister, Jenny, and a few years later, a brother, Harald, joined the family, too. In 1903, when he was 18 years old, Neils Bohr enrolled as an undergraduate student at the University of Copenhagen, majoring in physics. Two years later, his brother Harald joined him. The two Bohr brothers were always very close and both became influential professors at the University of Copenhagen; Neils in the field of physics and Harald in mathematics.

The Danish physicist Niels Bohr
Niels Bohr

In 1911, Bohr completed his education at the University of Copenhagen when he was awarded a Doctor of Philosophy (Ph.D.) in physics for his work on the behavior of electrons in a metal. Just a year later, he married Margrethe Norlund and they went on to have a total of 6 children, including one son, Aage, who would eventually win a Nobel Prize in physics, just like his father!

Niels Bohr, with his wife, Margrethe
Niels and Margrethe Bohr

After completing his Ph.D., Bohr taught for several years at Victoria University, but in 1916, he returned to the University of Copenhagen and it wouldn't be long before he made some major contributions to our understanding of the atom.

Bohr Model of the Atom

Niels Bohr was interested in understanding what was going on inside an atom. Atoms are so tiny that it was impossible to actually see inside them, especially back in the early 1900's. To figure out what was happening inside the atom, he had to study the way atoms behaved and then come up with a model that explained what was happening. In science, a scientific model is an idea about how nature works that can be tested and used to explain many observed phenomena.

Bohr studied the models of the atom that were already used by scientists and improved on them with a new model that better explained how atoms actually worked. His new model was named after him and is called the Bohr model of the atom. In the Bohr model, positively charged protons and neutral neutrons are tightly held in the nucleus, or center, of the atom. Negatively charged electrons move around the nucleus in defined orbits.

In the Bohr model of an atom, electrons move around the nucleus in designated orbits
Bohr Model

According to the Bohr model, electrons orbit the nucleus in defined locations, called shells. Some electron shells require the electrons to have more energy than others, so if an electron absorbs some energy, it can move into a higher energy shell. If it moves the other way, from a high energy orbit to a low energy orbit, it will emit a small packet of energy called a quantum.

This model explained the behavior of atoms very well. In particular, it explained why some elements tended to form chemical bonds more easily than others. Bohr said that atoms were most stable when the outer electron orbits were full. In most atoms, this means that they have eight electrons. Elements whose atoms already have a full outer electron shell are very stable and don't readily form bonds with any other atoms. Examples of these types of atoms are the noble gases, like neon and argon. If atoms don't already have eight atoms in their outer electron shell, they tend to bond with other atoms to complete the outer shell and be more stable. These types of atoms rarely exist on their own but are almost always bonded to others in order to maintain a full outer electron shell.

The first electron shell can contain two electrons, while the 2nd and 3rd can contain eight electrons. Atoms will form chemical bonds in order to maintain eight electrons in their outer shell.
bohr model and electron energy

Awards and Legacy

In 1922, Niels Bohr was awarded the Nobel Prize in physics for his work to advance our understanding of atomic structure. Even though he is best known for the development of the Bohr model of the atom, he also accomplished many other things in his lifetime. He spent many years studying the atomic nucleus and how it could be fissioned to release energy. His research was used in the development of atomic weapons and nuclear energy, and he spent much of his later life working to promote the peaceful development of nuclear energy and addressing problems that arose from the development of atomic weapons during World War II. In recognition of his efforts for the responsible use of atomic energy, in 1957, Niels Bohr was awarded the Atoms for Peace Award.

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