Subatomic Particles

by Ron Kurtus (revised 13 March 2016)

An atom is made up of subatomic particles: protons, neutrons, and electrons.

Protons and neutrons gather in an area at the center of the atom called the nucleus. Electrons are placed in shells around the nucleus.

Questions you may have include:

• What are protons?
• What are neutrons?
• What are electrons?

Protons

A proton has a positive (+1) electric charge.  It consists of two up quarks and one down quark, fundamental particles.

The mass of a proton is 1.673*10⁻²⁷ kg. Its relative mass is 1.007 amu.

The number of protons in the nucleus of an atom determines the atomic number of the element.

Neutrons

Neutrons have no electric charge. Every element except Hydrogen has at least one neutron in its nucleus. Other atoms have the same number or more neutrons as protons in the nucleus. Neutrons act as a form of binding force within the nucleus.

The mass of a neutron is 1.675*10⁻²⁷ kg. Its relative mass is 1.009 amu, slightly more than that of a proton.

The neutron is made up of one up quark and two down quarks.

Electrons

Electrons are considered fundamental or elementary particles. They are classified as leptons.

The mass of the electron is 9.109*10⁻²⁷ kg. Its relative mass is 5.489*10⁻⁴ amu

Electrons have a negative (−1) electric charge. In a stable atom (not an ion) the number of electrons equals the number of protons in the nucleus.

Electrons are set in "orbits" or shells around the nucleus. Another view is that they form a cloud around the nucleus.

Summary

An atom is made up of protons, neutrons, and electrons, which are considered subatomic particles.

Protons and neutrons gather in an area at the center of the atom, called the nucleus. Protons have positive (+1) electric charge, while neutrons are neutral. Electrons are placed in shells around the nucleus. They have a negative (−1) electric charge.

The number of electrons is usually the same as the number of protons in the atom.



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