This model basically looks like a little solar system, where the nucleus is the Sun and the electrons orbit the nucleus like the planets orbit the Sun . The solid behavior of atoms is due to the electromagnetic repulsion of the electrons in the outer orbits. When you strike your hand on a table, the solidness you feel is an illusion caused by the electrons pushing away from the atoms of the table and the atoms of your hand. Protons and neutrons are 1,860 times heavier than electrons. Virtually all the mass of the atom resides in the nucleus.
Heavy atoms tend to be radioactive.
The number of protons determines which chemical element the atom belongs to. This force between the protons and neutrons overcomes the repulsive electrical force that would, according to the rules of electricity, push the protons apart otherwise. Electrons Electrons are negatively charged subatomic particles, and they cause electricity when they flow, or static electricity when many of them build up in one place, or are taken away. The electrons have negative electrical charge, and their movement between atoms is responsible for electrical current . This is static electricity .