1. Protons: Positively charged particles located in the atom's nucleus. The number of protons determines the element.

2. Neutrons: Neutrally charged particles also located in the atom's nucleus. The number of neutrons can vary within an element, resulting in isotopes.

3. Electrons: Negatively charged particles that orbit the nucleus in a cloud-like region called the electron cloud. They are much smaller and lighter than protons and neutrons.

The nucleus, containing the protons and neutrons, is extremely dense and makes up almost all of the atom's mass. The electrons, while significantly lighter, occupy most of the atom's volume due to their orbital paths.