what is a neutron

A neutron is one of three main particles that make up the atom. The other two particles are the proton and electron. Atoms of all elementsexcept for most atoms of hydrogenhave neutrons in their nucleus. The nucleus is the small, dense region at the center of an atom where protons are also found. Atoms generally have about the same number of neutrons as protons. For example, all carbon atoms have six protons and most also have six neutrons. A model of a carbon atom is shown in the Figure 1.1. Click image to the left or use the URL below. URL:


properties of neutrons

Unlike protons and electrons, which are electrically charged, neutrons have no charge. In other words, they are electrically neutral. Thats why the neutrons in the diagram above are labeled n0 . The zero stands for zero charge. The mass of a neutron is slightly greater than the mass of a proton, which is 1 atomic mass unit (amu). (An atomic mass unit equals about 1.67 1027 kilograms.) A neutron also has about the same diameter as a proton, or 1.7 1017 meters.

same element different numbers of neutrons

All the atoms of a given element have the same number of protons and electrons. The number of neutrons, however, may vary for atoms of the same element. For example, almost 99 percent of carbon atoms have six neutrons, but the rest have either seven or eight neutrons. Atoms of an element that differ in their numbers of neutrons are called isotopes. The nuclei of these isotopes of carbon are shown in the Figure 1.2. The isotope called carbon-14 is used to find the ages of fossils. Q: Notice the names of the carbon isotopes in the diagram. Based on this example, infer how isotopes of an element are named. A: Isotopes of an element are named for their total number of protons and neutrons. Q: The element oxygen has 8 protons. How many protons and neutrons are there in oxygen-17? A: Oxygen-17like all atoms of oxygenhas 8 protons. Its name provides the clue that it has a total of 17 protons and neutrons. Therefore, it must have 9 neutrons (8 + 9 = 17).


particles in neutrons

Neutrons consist of fundamental particles known as quarks and gluons. Each neutron contains three quarks, as shown in the diagram below. Two of the quarks are called down quarks (d) and the third quark is called an up quark (u). Gluons (represented by wavy black lines in the diagram) are fundamental particles that are given off or absorbed by quarks. They carry the strong nuclear force that holds together quarks in a neutron.

instructional diagrams

No diagram descriptions associated with this lesson


atoms of all elements have neutrons in their nucleus.

a. true

-->  b. false

neutrons have a negative electrical charge.

a. true

-->  b. false

the mass of a neutron is close to the mass of

a) an electron.

-->  b) a proton.

c) the nucleus.

d) none of the above

a neutron has about the same diameter as a proton.

-->  a. true

b. false

atoms of the same element may differ in their numbers of neutrons.

-->  a. true

b. false

each neutron contains

-->  a) three quarks and three gluons.

b) two up quarks and one down quark.

c) two quarks and one gluon.

d) two gluons and one quark.

diagram questions

No diagram questions associated with this lesson