Proton

Proton, pronounced PROH tahn, is a positively charged subatomic particle. A single proton constitutes the nucleus of an ordinary hydrogen atom. Protons, together with other subatomic particles called neutrons, make up the nuclei of all other atoms. All atoms of the same chemical element have the same number of protons. The number of protons in the atoms is called the atomic number of the element.

Ordinarily, an atom has an equal number of protons and electrons, negatively charged particles that surround the nucleus. Each proton carries one unit of positive charge, and each electron carries one unit of negative charge. As a result, the atom is electrically neutral.

Protons are made up of fundamental particles called quarks. A proton has a diameter of approximately 1/25,000,000,000,000 inch (0.000000000001 millimeter). The mass of a proton in grams may be written with a decimal point followed by 23 zeros and a 2.

The proton was first identified by the German physicist Wilhelm Wien in 1902, and its identity was proven by the British physicist Sir Joseph J. Thomson in 1906. Scientists initially believed that protons would not naturally decay (break down) into other particles. However, mathematical grand unified theories, introduced in the mid-1970's, offered new insights about the fundamental forces that affect atoms and their nuclei. These theories predict protons can decay. Experiments to detect this decay are underway.

Contributor: Edward S. Fry, Ph.D., Prof. of Physics, Texas A&M Univ.

Proton

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