The 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 1900s. 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, while negatively charged electrons move around the nucleus in defined orbits.
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.
Niels Bohr's Awards & 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.
Bohr served as the director of the Institute for Theoretical Physics at the University of Copenhagen for many years, and after his death, it was renamed the Niels Bohr Institute. He also played an instrumental role in the founding of the European Institute for Nuclear Research, better known as CERN, where some of the world's most cutting-edge physics research is still going on, as well as providing good fodder for thriller novels and films like Dan Brown's Angels and Demons. Today, CERN is the site of the Large Hadron Collider, the largest particle accelerator in the world. Researchers from all over the world come to CERN to investigate nuclear and particle physics.
Lesson Summary
Let's now take a moment or two to review. As we learned in this lesson, Niels Bohr was a Danish physicist who is most famous for developing a scientific model, which is an idea about how nature works that can be tested and used to explain many observed phenomena, involving the atom.
In what became known as the Bohr model, neutrons and protons are held together in the nucleus of the atom, while electrons orbit the nucleus. Electrons orbit in well-defined locations, called shells, that correspond to specific amounts of energy. As atoms absorb energy, electrons can move to a higher energy orbit, and if electrons move from a high energy orbit to a low energy orbit, they emit a small packet of energy, known as a quantum.
Bohr's model also explained why some atoms usually formed chemical bonds with other atoms while others didn't. In the Bohr model, atoms will tend to form bonds in order to have a full, stable outer shell of electrons. Atoms that already have a full outer electron shell will not form bonds with other atoms, while atoms without a full outer electron shell will readily form bonds with other atoms in order to maintain a full outer electron shell.
Bohr was awarded the Nobel Prize in 1922 for the development of the Bohr model. He also played a large role in the development of atomic weapons and nuclear energy, and, in 1957, was awarded the Atoms for Peace Award for his efforts in the responsible use of atomic energy. He was the founder and director of the Institute for Theoretical Physics at the University of Copenhagen and was part of a group of scientists who founded CERN, where much of the world's nuclear and particle physics research goes on today, with things like the famous Large Hadron Collider.
