Electrons and protons are not located in the exact middle of an atom. The structure of an atom is often depicted using a simplified model called the Bohr model or the Rutherford-Bohr model, which represents the electrons as orbiting around the nucleus in specific energy levels or shells. In this model, the protons and neutrons are located in the nucleus at the center of the atom.
The reason why electrons are shown to be orbiting around the nucleus is due to their behavior as described by quantum mechanics. Electrons possess both particle-like and wave-like properties, and their behavior is best described by the concept of electron orbitals or electron clouds. These orbitals represent regions in space where electrons are likely to be found.
The specific arrangement of electrons in an atom is determined by the atom's electronic structure, which follows certain rules and principles such as the Pauli exclusion principle and Hund's rule. These rules govern how electrons occupy different energy levels or orbitals around the nucleus.
It's important to note that the electron cloud is not a physical object with a distinct boundary or fixed position. The electrons exist in a probabilistic "cloud" of charge, and their precise location within the cloud is uncertain. Therefore, it is more accurate to describe the location of electrons in terms of their probability distributions rather than as fixed points.