Atoms also contain small particles called electrons. The electron orbits the outside of the nucleus. Sometimes the outermost electrons of an atom may become attracted to other types of elements and can unite by sharing, receiving or giving electrons. Elements like metals, forfeit their electrons more readily making them much better conductors of electricity and heat.

Some of the particles of an atom have an electrical charge. A proton has a positive charge +1, a neutron has no charge and an electron a negative charge of -1. A stable atom has a net charge of 0. That means it has an equal number of protons and electrons. The positive proton cancels out the negative electrons. If the number of electrons does not equal the number of protons, the atom is ionized and called an ion. A radioactive atom occurs when its nucleus has too many of too few neutrons.

Nuclear Energy

A scientist named Enrico Fermi came to the United States after receiving the Nobel Prize for physics in Sweden in 1938. Fermi and other scientist believed huge amounts of energy were released when mass was changed into energy during nuclear fission. Albert Einstein's mass-energy equation E=mc2, describes this change of mass energy to kinetic energy. After convincing President Roosevelt of their discovery, Femi was appointed to head a research team whose secret project was to develop an atomic bomb. Fermi's job was to create a controlled nuclear reaction in which the atom is split without creating a dangerous explosion.

During nuclear fission, a neutron is fired at an atom's nucleus, which splits and releases a neutron. The neutron that is released can go on to split another nucleus, releasing another neutron and so on over and over again. If this happened to fast, an explosion would occur. Yet, if this reaction could be controlled, it could produce a steady flow of energy.

In December of 1942 at the University of Chicago, Fermi tested his theory for first time. If he was wrong, they could have blown up most of Chicago! As you probably guessed, the first controlled nuclear reaction from a source other than the sun was accomplished that day. Since then, Fermi's theory has been expanded and improved.

Nuclear reactions are used in many different ways. The fission (splitting) of nuclei and the fusion (combining) of nuclei both result in energy being released. Fission energy is used to generate electricity. Someday, scientist may be able to actually turn fusion energy into electricity. The fusion process is also how the sun and other stars are powered. On earth though, very high temperatures are needed to make fusion occur. Fission and fusion reactions are also used in nuclear weapons, using an uncontrolled nuclear reaction resulting in atomic and hydrogen bomb explosions. Nuclear power also can be dangerous because of the waste products produced.

Quarks? How Low Can We Go!

The first particle of an atom to be discovered was the electron in 1898! Ernest Rutherford discovered that the nucleus of an atom was very dense, or extremely packed together. If the earth were as dense as the nucleus of an atom, its diameter would only be about 1/3 mile or 0.5 kilometers! Rutherford also discovered the nucleus contained a particle which he named proton. In 1932, James Chadwick discovered another particle in the nucleus known as the neutron.

Before 1963, scientist believed they had found the smallest particle of an atom. Murray Gell-Mann had a theory in 1963, that each proton and neutron was made up of three even smaller particles named quarks!

Quarks make up protons and neutrons which make up an atom's nucleus. Each proton and neutron have three quarks. There are different kinds of quarks but protons and neutrons just have up and down quarks. The quarks have electrical charges.

Each up quark has a charge of +2/3
Each down quark has a charge of -1/3

The sum of the quark charges, determine the charge of the nuclear particle. It sounds difficult, but watch:

Protons have two up quarks and one down quark. (+2/3 ) plus (+2/3 ) plus (-1/3) = +1

Neutrons have one up quark and two down quarks. (+2/3) plus (-1/3) plus (-1/3) = 0 Now can you see why protons have an electrical charge of +1 ? And why neutrons have no charge!