Electrons do not enter the atomic nucleus because they have a negative charge and are governed by the electromagnetic force. The nucleus, on the other hand, contains positively charged protons and uncharged neutrons, and is held together by the strong nuclear force.
The electron is a subatomic particle that orbits around the nucleus in specific energy levels or electron shells. These energy levels are quantized, meaning electrons can only occupy certain discrete energy states. The behavior of electrons within atoms is described by quantum mechanics.
In an atom, the negatively charged electrons are attracted to the positively charged nucleus due to the electromagnetic force. This force of attraction between opposite charges keeps the electrons in orbit around the nucleus. The electromagnetic force is much stronger than the gravitational force and is responsible for the stability and structure of atoms.
However, it's important to note that electrons cannot exist within the nucleus itself. The space occupied by the electrons and the space occupied by the protons and neutrons within the nucleus are distinct and separated. The size of the nucleus is much smaller compared to the electron cloud surrounding it.
In summary, electrons do not enter the atomic nucleus because they are negatively charged particles governed by the electromagnetic force, while the nucleus contains positively charged protons and uncharged neutrons, and is held together by the strong nuclear force.