The electrons in an atom are held in orbit around the nucleus by the electromagnetic force, specifically through the concept of electrostatic attraction.
According to the laws of quantum mechanics, electrons exist in specific energy levels or shells around the nucleus of an atom. These energy levels are represented by quantum numbers and can be thought of as orbitals or probability clouds where electrons are most likely to be found.
The nucleus of an atom contains positively charged protons and uncharged neutrons. Since opposite charges attract each other, the positively charged nucleus exerts an attractive force on the negatively charged electrons. This force of attraction is the electrostatic force.
The electrostatic force between the nucleus and electrons keeps the electrons in their respective energy levels or orbitals. The electrons occupy the lowest available energy levels first, following a set of rules known as the Aufbau principle, Pauli exclusion principle, and Hund's rule. These rules determine the arrangement and distribution of electrons in different orbitals.
It's important to note that the concept of electrons orbiting the nucleus in a classical sense, akin to planets orbiting the sun, is an oversimplified analogy. In reality, electrons in atoms exist as waves of probability, and their behavior is described by quantum mechanics. The electron cloud or orbital represents the region where the electron is most likely to be found, rather than a well-defined circular path.
In summary, the electrostatic attraction between the positively charged nucleus and negatively charged electrons is what holds the electrons in orbit around the nucleus of an atom.