The nucleus is a compact and dense region in the centre of the atom that makes up for most of
its mass. It is made up of a group of subatomic particles known collectively as nucleons. The two
states of nucleons are protons and neutrons.
Although the electron, and not the nucleus, is responsable for chemical reactions, the nucleus
still holds much information about the atom. Since nucleons are about 2000 times heavier than electrons,
the mass of the nucleus is approximately equal to the mass of the atom. The number of protons in the
nucleus determines the type of atom, and nuclear charge is the property by which the elements are arranged
in the periodic table.
A tremendous amount of energy is used to hold the nucleus together, since the repulsion between
the positively charged protons is great. The bonding forces that hold the nucleus together are collectively
known as the nucleur forces. When heavy element nuclei are split into smaller nuclei, or light element
nuclei combined to make one nucleus, tremendous energies are released. The former is known fission, and
the latter, fusion, and they are the driving forces behind stars and nuclear weopons.
From Dalton's theory, it was thought that atoms were indivisible particles that made up everything
in the world. When Rutherford made his gold foil experiment, however, he found that when high-velocity
positive alpha particles bombarded a thing metal foil, while most passed straight through, some were
reflected back or deflected. This led him to postulate that most of the atom was empty space, with most
of the mass concentrated in one dense region in the centre of the arom. Thus, most of the positive
alpha particles passed through the empty space, but some hit the dense core and were reflected
back by electric repulsion. He called this the nucleus of the atom.
Subsequently, improvements were made on the Rutherford model. The nucleu was theorized to contain
both positive and neutral particles.
The interactions in the nucleus, the strong and the weak
forces, are the strongest forces in nature. Processes
such as fission and fusion release much of this energy,
and make possible new energy sources. In fact, fusion
is the process by which stars generate light and heat,
and thus the source from which all life on earth is derived.
Other processes, such as radiation, have medical applications.