Chlorine is a chemical element (symbol Cl) and a member of the halogen family, Group 17 on the periodic table. It exists naturally as a diatomic molecule (Cl2), where two chlorine atoms are bonded together. This highly reactive element is fundamental to industrial chemistry, used extensively in the production of consumer goods, from plastics like PVC to various solvents and disinfectants. Understanding its physical properties, particularly phase change temperatures, is important for safe storage and application.
The Specific Boiling Point of Chlorine
The boiling point of chlorine, the temperature at which it turns into a gas, is significantly below the freezing point of water. Chlorine boils at approximately -34.04°C at standard atmospheric pressure. This measurement converts to 239.11 K on the Kelvin scale. In the Fahrenheit system, this temperature is equivalent to about -29.27°F.
Chlorine’s Natural State and Physical Appearance
This low boiling point dictates that chlorine exists naturally as a gas under standard room temperature and pressure conditions. Elemental chlorine is visually identified by its distinct pale yellow-green color. The element’s name is derived from the Greek word khlôros, meaning “yellowish-green,” reflecting this characteristic.
Chlorine gas is considerably denser than air, being about two and a half times heavier, and tends to settle in low-lying areas if released. It is known for its intensely pungent, choking odor, which can be detected even at very low concentrations.
The gas is highly toxic and corrosive, capable of causing severe irritation to the respiratory system. Chlorine is typically stored and transported as a pressurized, compressed liquid. Maintaining the temperature below its boiling point is necessary to keep it in the liquid phase for safe, efficient storage.
The Molecular Forces Behind the Boiling Point
The specific boiling point of chlorine is determined by the weak attractive forces between its Cl2 molecules. Since the two identical chlorine atoms share electrons equally, the Cl2 molecule is nonpolar. Therefore, the molecules are held together only by London Dispersion Forces (LDF), a type of Van der Waals force.
London Dispersion Forces result from temporary, instantaneous shifts in electron distribution. The ease with which the electron cloud of a molecule can be distorted to create these temporary dipoles is called polarizability. Since chlorine is a larger molecule than the lighter halogen, fluorine (F2), it possesses more electrons and is more polarizable.
This greater polarizability means the London Dispersion Forces are stronger in chlorine than in fluorine, which explains why chlorine has a higher boiling point than F2. Conversely, chlorine is smaller and has fewer electrons than the next halogen, bromine (Br2). Because Br2 is more polarizable, its stronger dispersion forces result in a higher boiling point.