Neutron
A neutron is an electrically neutral subatomic particle found in the nucleus of all atoms except ordinary hydrogen, with a mass of approximately 1.675 × 10⁻²⁷ kg, slightly greater than the proton. Neutrons contribute to the mass of the nucleus and play a crucial role in nuclear stability by reducing electrostatic repulsion between protons through the strong nuclear force. Atoms with the same number of protons but different numbers of neutrons are called isotopes.
Key Formula
N = A - Z (Number of neutrons = Mass number - Atomic number)
LaTeX: N = A - Z
| Symbol | Meaning | Unit |
|---|---|---|
| N | Number of neutrons | dimensionless |
| A | Mass number (total protons + neutrons) | dimensionless |
| Z | Atomic number (number of protons) | dimensionless |
Worked Example
Problem
Carbon-14 has an atomic number of 6 and a mass number of 14. How many neutrons does it have?
Solution
Step 1: Use the formula N = A - Z. Step 2: Substitute values: N = 14 - 6. Step 3: Calculate: N = 8.
Answer
Carbon-14 has 8 neutrons.
Properties of the Neutron
| Property | Value | Unit |
|---|---|---|
| Charge | 0 | Elementary charge (e) |
| Mass | 1.6749 × 10⁻²⁷ | kg |
| Mass (amu) | 1.0087 | u |
| Location | Nucleus | — |
| Composition | 1 up quark + 2 down quarks | — |
| Half-life (free neutron) | ~881.5 | seconds |
Interactive Tools
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Related Terms
Proton
A proton is a positively charged subatomic particle found in the nucleus of every atom, with a charge of +1 elementary charge and a mass of approximately 1.673 × 10⁻²⁷ kg (about 1 atomic mass unit). The number of protons in an atom's nucleus defines the element and is called the atomic number, which determines the chemical identity of the atom. Protons are composed of two up quarks and one down quark held together by the strong nuclear force.
Isotope
Isotopes are atoms of the same element (same atomic number Z) that have different numbers of neutrons, resulting in different mass numbers (A) but identical chemical behavior. Some isotopes are stable while others are radioactive (radioisotopes) and undergo decay, emitting radiation until they reach a stable configuration. Isotopes have widespread applications in medicine (radioactive tracers, cancer treatment), archaeology (radiocarbon dating), and nuclear energy.
Mass Number
The mass number (symbol A) is the total number of nucleons — protons and neutrons — in the nucleus of an atom, and is always a whole number. It is used to distinguish between different isotopes of the same element, as isotopes have the same atomic number (Z) but different mass numbers (A) due to differing neutron counts. The mass number is approximately equal to the atomic mass in atomic mass units (u), though not exactly because of binding energy effects.
From Latin "neuter" meaning "neither" (neither positive nor negative), reflecting its neutral charge. The neutron was discovered by James Chadwick in 1932, who named it based on its electrical neutrality. The discovery completed the picture of nuclear composition.