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).
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.
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
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
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
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
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 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 (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 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