Page 14 - Curriculum Visions Dynamic Book

(Below) It takes a lot
of energy to break the hydrogen bonds in water and allow evaporation or boiling to take place.
(Above) The thermal capacity of water partly relates to its hydrogen bonds. The energy used in melting the ice in this ice cooling jacket partly comes from the bottle it encloses. This cools the bottle.
The effect of linking molecules is very important. Normally, a liquid made of small molecules flows freely and boils easily. But water is not like that. The bonding makes water “thicker” or “stickier” (more viscous)
than it would otherwise be. It also means that the surface holds together as though it had an invisible skin (called surface tension). It also boils at a much higher temperature (100°C) than would otherwise be expected (without the bonding it would boil at –100°C!). So water would not exist as solid or liquid on Earth at all and would be more like carbon dioxide or oxygen gases.
Radioactive water
Many elements can exist in different forms called isotopes. Sometimes the isotopes are radioactive. Isotopes of hydrogen include 2H, or D, deuterium,
and 3H, or T, tritium. These isotopes combine with oxygen and form water molecules. Heavy water is D2O, deuterium oxide. Heavy water and tritium can be combined to release enormous amounts of energy and can be used in the making of nuclear bombs.
Deuterium can also be used to slow down the neutrons produced in a nuclear reaction. A material that can do this is called a “moderator.” Heavy water can be used as a moderator. Heavy water is a poor absorber of neutrons, and that allows heavy water reactors to use natural (nonenriched) uranium as a fuel.
14