The subatomic particles that form a cloud around the nucleus are called electrons. In an atom, the nucleus is made up of protons and neutrons, while the electrons exist in regions of space surrounding the nucleus, often referred to as electron shells or orbitals.
Electrons are negatively charged particles, and their movement around the nucleus creates a ‘cloud’ of probability density where they are most likely to be found. This cloud represents the various energy levels at which electrons can exist, and it plays a crucial role in determining the chemical properties of an atom.
The behavior of electrons is often described by quantum mechanics, which tells us that they do not have precise positions but rather exist in a state of probability. This means that the electron cloud can be visualized as a fuzzy region around the nucleus where the likelihood of finding an electron at any given time varies.