What Keeps Electrons in Their Orbit Around the Nucleus?

The simple atomic model is beginning to show its age as newer, more accurate models become commonplace.

Science is a discipline built on constant change. Modern atomic theory is relatively new, with roots barely a century old, yet in that short time, it has undergone radical changes. These changes render older models obsolete or inadequate to fully explain what is going on inside the atom. To answer why the electrons stay in their orbit around he nucleus is a complex undertaking which requires learning more about the very nature of matter itself.

Elementary Model of the Atom

The elementary model of the atom (often called the Bohr model) is depicted very similarly to a diagram of the solar system. In this model, the dense nucleus comprised of electrically neutral neutrons and positively charged protons are surrounded by negatively charged electrons. These electrons are displayed as circling the nucleus like planets around the dense nuclear "sun." However, this model is (at best) an incomplete picture of what is going on within the atom. This model misses many key features to describe the atom accurately.

Dual Nature of the Electron

The electron is a strange entity. Under some circumstances, it can act like a particle, yet under others, it acts like a wave. In a copper wire, electricity is the movement of a collection of discrete electrons (each acting like a particle). In experiments where scientists pass them through slits, however, electrons create patterns of interference that could only be accomplished if they were acting as waves. Because of this, any model which views the electron as a wave or particle (and not both) is incomplete.

Heisenberg's Uncertainty Principle

Heisenberg was a German scientist who discovered a relationship between position and momentum that can be summed up most simply by stating there is a limit to how closely you can know something. In other words, by the very act of trying to measure information about an electron, you change it. This means that any model that tries to depict the electron as maintaining a singular orbit is inaccurate. A proper model of the atom must consider the uncertain nature of the electron in position and energy, as well as form.

Modern Atomic Model

The modern atomic model displays electrons as existing in cloud-like orbitals rather than elliptical orbits. The reason for this is because the uncertainty of position and form of the electron is best described by a probability formula. While the positive charge of the protons in the nucleus cause an electrostatic pull that attracts the electron cloud, it is insufficient to cause the electron cloud to collapse. In short, the kinetic energy of the electron cloud is balanced against the electrical energy that pulls it toward the nucleus. The orbit is maintained because it would require more energy to pull the electron cloud into the nucleus than the electrical charge can provide.

References

• Wave particle duality
• SEP: The Uncertainty Principle
• Electron Orbits
• Chemguide: ATOMIC ORBITALS

Resources

• UofI:Q & A: Why do electrons move?