Water is the standard other substances are compared to on the Celsius temperature scale. The Celsius scale, also called the centigrade scale, is based on water. Water freezes at 0 degrees Celsius and boils at 100 degrees Celsius. The interesting thing about water is that warm water freezes faster than cold water. This is because when water freezes, its molecules line up in a hexagon, or six sided arrangement, like a bee's honeycomb. Cold water molecules are packed tightly together, whereas warm water molecules are already nearly in a honeycomb pattern. The warm water molecules have less distance to travel to line themselves up, so warm water freezes faster. The six sided pattern can be seen in snowflakes and ice crystals.
The freezing point of a substance is the point where a liquid becomes a solid. When a substance is frozen, all the molecules line up in regular patterns. Because different substances have different molecular structures, the freezing points are different. Substances with a lot of molecules, take a long time for all the molecules to line up. One unique gas, carbon dioxide, has only a few molecules, but these are lined up almost like a solid. Carbon dioxide freezes directly from a gas into a solid. The common name for frozen carbon dioxide is dry ice.
Molecules also have a strength factor, which is a measure of how strongly each molecule is attached to others. The weaker the bond, the lower the freezing point. Physicists at the University of Illinois state that liquid nitrogen, because of a weak bond, freezes solid at -209.86 degrees Celsius. Benzene, a flammable liquid, has strong bonds so it freezes at 5.5 degrees Celsius.
Researchers at the Massachusetts Institute of Technology (MIT) investigated the transition phase when a liquid turns into a solid in January of 2011. This temperature window was not well understood. Reporter David L. Chandler said the fine line when a liquid turns into a solid is difficult to measure. Researchers discovered that a thickening phase exists before freezing, when a liquid actually starts to become thicker, like a syrup. As of 2011, the research is still in the preliminary phase, so long term applications for this discovery are unknown.