What is the nucleus?
Q: What is the nucleus?
A: The nucleus is the center of an atom, made up of nucleons called protons and neutrons and surrounded by the electron cloud.
Q: What is the size (diameter) of a nucleus?
A: The size (diameter) of a nucleus ranges from 1.6 fm (10−15 m) (for a proton in light-weight hydrogen) to about 15 fm (for the heaviest atoms, such as uranium). These sizes are much smaller than the size of the atom itself by a factor of about 23,000 (uranium) to about 145,000 (hydrogen).
Q: Does most of an atom's mass come from its nucleus?
A: Yes, almost all of an atom's mass comes from its protons and neutrons in its nucleus. Only a small amount comes from its orbiting electrons.
Q: Are protons positively charged?
A: Yes, protons are positively charged while neutrons have no electric charge. Because it is only made up of protons and neutrons, the nucleus has a positive charge.
Q: Why doesn't electromagnetic force cause nuclei to break apart?
A: Things that have the same charge repel each other; this repulsion is part of what is called electromagnetic force. However, something else holds together nuclei so they don't break apart - this force is known as strong nuclear force.
Q: When was "nucleus" first used in atomic theory? A: Ernest Rutherford proposed using "nucleus" for atomic theory in 1912; however it wasn't until 1916 when Gilbert N Lewis wrote his famous article The Atom and Molecule that "the atom is composed of kernel and outer shell".
