Atoms are composed of three primary subatomic particles: protons, neutrons, and electrons.
Protons carry a positive electrical charge and are found in the nucleus, which is located at the center of the atom. Each proton has a relative mass of approximately 1 atomic mass unit (amu).
Neutrons, on the other hand, are electrically neutral particles also found in the nucleus of an atom. They have a relative mass similar to protons, approximately 1 amu.
Electrons are negatively charged particles that orbit the nucleus in specific energy levels or shells. They are much smaller and lighter than protons and neutrons, with a relative mass of about 1/1836 amu.
In summary, the nucleus of an atom contains protons and neutrons, while electrons occupy the space outside the nucleus in different energy levels. The number of protons determines the atomic number of an element, while the sum of protons and neutrons gives the atomic mass.