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What Is a Subatomic Particle? - Definition & Mass

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  • 0:47 Examples: What's…
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Lesson Transcript
Instructor: Elena Cox
A subatomic particle is a particle smaller than an atom. Learn more about how to identify subatomic particles through several examples, and test your knowledge with quiz questions.

Definition

A subatomic particle is a unit of matter or energy that's the fundamental makeup of all matter. According to modern atomic theory, an atom has a nucleus, which is its center, or core.

The nucleus contains subatomic particles: protons and neutrons. Protons are positively-charged particles. Neutrons are neutral particles. Surrounding the nucleus is a cloud of very small subatomic particles called electrons. Electrons are negatively-charged particles.

But these basic atomic components are by no means the only known subatomic particles. However, quarks, muons and neutrinos, which make up major subatomic particles, will not be covered in this lesson.

Examples: What's Inside an Atom?

An atom is one of the smallest particles in nature. Matter is made up of atoms. Atoms have three basic parts: neutrons, electrons and protons. The neutrons and protons are found in the center of the atom. The electrons circle around the protons and neutrons in a cloud, as shown in this figure. The particles represented in the figures are not shown in their correct proportions because the electrons would be too small to see.

Let's look at the structure of the atomic nucleus to understand the nature of subatomic particles. The nucleus inside an atom consists of positively-charged protons and neutrally-charged neutrons.

A proton is a subatomic particle with a positive electric charge. All protons are identical. The mass of a proton is approximately 1.6726 * 10^-24 g. Because the masses of particles in atoms are so small, scientists developed a new unit for them. The SI unit known as the atomic mass unit, abbreviated amu, is used to express the masses of subatomic particles. Scientists assign each proton a mass of 1 amu and symbol 'p.' All protons are identical, no matter from which kind of element they come. All the atoms of one element have the same number of protons.

Neutrons are the particles of the nucleus that have no charge. All neutrons are identical. Neutrons, with the mass of 1.674928 * 10^-24 g, are slightly more massive than protons, but the difference in mass is so small that neutrons are also given an atomic mass of 1 amu. A neutron has slightly more mass than a proton. Each has almost 2,000 times the mass of an electron. Neutrons have the symbol 'n.'

Let's consider some interesting facts about neutrons. Neutrons are very penetrative subatomic particles - more penetrative than gamma rays and can penetrate several centimeters into several materials. Neutrons escaping from a nuclear fission reaction can even penetrate the human body. They are among the most biologically-destructive of nuclear fission products and can be very damaging to cells. Some elements, like hydrogen, capture and scatter neutrons. Water is commonly used as a neutron radiation shield.

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