Hydrogen has three isotopes. The nucleus of a "normal" hydrogen atom has one proton (red) but no neutrons (blue). Hydrogen's other isotopes are deuterium (1 proton + 1 neutron) and tritium (1 proton + 2 neutrons).
Click on image for full size
Original artwork by Windows to the Universe staff (Randy Russell).

Isotope

Isotopes are different "versions" of an element. All atoms of an element have the same number of protons. For example, all hydrogen atoms have one proton, all carbon atoms have 6 protons, and all uranium atoms have 92 protons. However, atoms of an element can have different numbers of neutrons. Most carbon atoms have 6 neutrons, but about 1% of the carbon atoms on Earth have 7 neutrons. All carbon atoms have an atomic number (number of protons) of six, but these two different isotopes of carbon have an atomic mass (number of protons + neutrons) of 12 or 13.

Scientists use special "codes" to write the names of isotopes. One isotope of carbon has 8 neutrons. It has an atomic mass of 14 (6 protons + 8 neutrons). The "code" for this isotope is carbon-14 or 14C. Different isotopes of the same element behave almost exactly the same way in chemical reactions. For example, most oxygen is the isotope oxygen-16. Oxygen-18 is a rare isotope. However, adding two hydrogen atoms to one oxygen atom still makes water (H2O), even if we use 18O instead of 16O. Some isotopes are radioactive, but others are not. Radioactive isotopes can "decay" by giving off radiation.

Where do different isotopes come from? Astronomers think the only elements created in the Big Bang were various isotopes of hydrogen, helium, and probably lithium, beryllium and boron. Supernova explosions created the rest of the elements, including most of their isotopes. Some isotopes form when high-energy cosmic rays crash into atoms in our atmosphere.

Isotopes help scientists learn about the history of some natural events. Carbon dating techniques help us figure out how old some objects are. Oxygen isotopes help us learn about past climates. Some of the water molecules in ice have the rare oxygen-18 isotope in them. The mix of 18O and 16O in ice core samples from Greenland and Antarctica give us clues about Earth's temperature in the past.

Last modified August 26, 2009 by Randy Russell.

You might also be interested in:

Traveling Nitrogen Classroom Activity Kit

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Element (Chemical Element)

An element (also called a "chemical element") is a substance made up entirely of atoms having the same atomic number; that is, all of the atoms have the same number of protons. Hydrogen, helium, oxygen,...more

Atomic Number

The nucleus of an atom has protons and neutrons in it. Each element (like carbon or oxygen or gold) has a different number of protons in its atoms. Scientists have a special name for the number of protons...more

Atomic Mass

One way scientists measure the size of something is by its mass. Scientists can even measure very, very tiny things like atoms. One measure of the size of an atom is its "atomic mass". Almost all of the...more

Radioactive Decay

Some materials are radioactive. They emit radiation. When an atom of a radioactive substance gives off radiation, it becomes a new type of atom. This process is called radioactive decay. There are two...more

Radiation

Radiation comes in two basic types: electromagnetic radiation transmitted by photons, and particle radiation consisting of electrons, protons, alpha particles, and so forth. Electromagnetic radiation,...more

Carbon-14 Dating

Carbon-14 dating (also called "radiocarbon dating") is used to determine the age of materials that contain carbon that was originally in living things. It is often used in archeology and some...more

Carbon-14

Carbon-14 is an isotope of the element carbon. All carbon atoms have 6 protons in their nucleus. Most carbon atoms also have 6 neutrons, giving them an atomic mass of 12 ( = 6 protons + 6 neutrons). Carbon-14...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA