The particles that orbit the center of an atom are electrons. Electrons are negatively charged subatomic particles that revolve around the nucleus of an atom in specific energy levels or orbitals. The nucleus, located at the center of an atom, consists of positively charged protons and usually uncharged neutrons.
According to the Bohr model of the atom, electrons occupy discrete energy levels or shells, which are represented by whole numbers (1, 2, 3, etc.). The innermost shell, closest to the nucleus, can hold a maximum of two electrons, while the subsequent shells have higher capacities. The distribution of electrons in these energy levels is based on the principle that electrons fill the lower energy levels before moving to higher energy levels.
However, it's important to note that the behavior of electrons is better understood through the quantum mechanical model of the atom, which describes the electron cloud or probability distribution of electrons around the nucleus. In this model, electrons are considered to exist in regions called orbitals, which are three-dimensional regions of space where electrons are likely to be found.
The concept of electron orbitals is more complex than the classical idea of electrons orbiting the nucleus in a fixed path, as it incorporates wave-particle duality and the uncertainty principle. The electron cloud represents the probability distribution of finding an electron within a particular region around the nucleus, rather than a fixed path or trajectory.