Heavy Water
Definition and meaning of Heavy Water in chemistry.
Heavy water is a special type of water where both hydrogen atoms are a heavier isotope called deuterium. It has the chemical formula D2O instead of the usual H2O. This unique makeup slightly changes its physical properties.
In more detail
A normal hydrogen atom has just one proton in its center and zero neutrons. A deuterium atom has one proton and one neutron in its core. This extra neutron makes the deuterium atom twice as massive as normal hydrogen.
Because of this, heavy water is about eleven percent denser than ordinary liquid water. An ice cube made of heavy water will actually sink in a glass of normal water. Heavy water also has slightly different temperatures for its phase changes.
It boasts a higher boiling point of exactly 101.4 degrees Celsius. It freezes at 3.8 degrees Celsius instead of the usual zero degrees. Deuterium is a naturally occurring isotope, but it is very rare in nature.
Only one in every 6,400 hydrogen atoms on Earth is deuterium. Most natural water has just a tiny bit of it mixed into the liquid. Factories must purify normal water in massive amounts to get pure heavy water.
They often use a complex chemical method called the Girdler sulfide process. They can also use electricity to slowly separate the heavier water molecules. Heavy water is incredibly important for running certain nuclear power plants.
The massive deuterium atoms are great at slowing down fast-moving neutrons. This helps carefully control the nuclear chain reaction without stopping it completely.
Key facts
| Field | Physical Chemistry |
|---|---|
| Formula | D2O |
| Molar mass | 20.03 g/mol |
| Boiling point | 101.4 °C |
| Melting point | 3.8 °C |
In a Canadian CANDU nuclear reactor, heavy water surrounds the radioactive uranium fuel rods. The liquid heavy water acts as a coolant and slows the flying neutrons down. Slower neutrons are much more likely to hit other uranium atoms and split them. This clever design lets the reactor run on natural uranium without needing enriched fuel.
Frequently asked questions
Is heavy water radioactive?
No. Deuterium is a perfectly stable and natural isotope of hydrogen. Heavy water's strange effects come from its extra mass, not from any radiation.
Is drinking heavy water dangerous for humans?
A small amount is harmless and passes through your body. However, drinking a large amount can be toxic because the heavier atoms slow down important biological reactions.
Does heavy water look or taste different?
Heavy water looks exactly like normal clear water. Some people report that it has a very slightly sweeter taste, but it is mostly tasteless.
Related terms
Sources & references
See our sources and editorial standards.