Chlorine (Cl) is a highly reactive element with an atomic number of 17, belonging to the halogen group on the periodic table. As a diatomic molecule, Cl2, it is a fundamental chemical agent used widely across global industries and in everyday life. Understanding its physical constants, such as the temperatures at which it changes state, is necessary for its safe storage, handling, and industrial application.
The Melting Point of Chlorine
The melting point of chlorine is measured at approximately \(-101.5 \text{ }^\circ\text{C}\). This temperature signifies the boundary where solid chlorine transitions into its liquid form under standard atmospheric pressure. Below this point, the element exists as a pale yellow crystalline solid. This low melting point is characteristic of many diatomic molecules, indicating that the element has very weak intermolecular forces that are easily overcome by heat.
Properties of Chlorine Gas
At standard room temperature and pressure, chlorine is a gas. This gaseous form is recognizable by its distinct yellow-green color, a feature that gave the element its name from the Greek word khlôros, meaning “yellowish-green.” The gas is also significantly heavier than air, being about two and a half times denser. This density means it tends to settle in low-lying areas, which is a factor in safety protocols, as is its pungent, bleach-like odor.
Chlorine gas is acutely toxic; inhaling even small concentrations can cause severe irritation to the respiratory system. Its danger stems from its high chemical reactivity, specifically its role as a powerful oxidizing agent. This oxidizing potential means that chlorine readily reacts with other elements and compounds by stripping away electrons. This property is the source of both its industrial utility and its hazardous nature.
Related Phase Transitions
The boiling point of chlorine occurs at about \(-34.0 \text{ }^\circ\text{C}\), which is the temperature where the liquid state converts into the gaseous state. Therefore, chlorine exists as a liquid between its melting point of \(-101.5 \text{ }^\circ\text{C}\) and its boiling point.
In its liquid state, chlorine is a dense, clear amber-colored substance. Since the boiling point is well below the freezing point of water, chlorine must be cooled or pressurized to maintain its liquid form for commercial transport and storage. This process, known as liquefaction, allows large quantities of the element to be stored efficiently. The narrow temperature range of approximately \(67.5 \text{ }^\circ\text{C}\) between its melting and boiling points highlights its volatility at ambient temperatures.
Common Applications of Elemental Chlorine
The strong chemical reactivity of chlorine is harnessed for numerous practical purposes across various sectors. One of its most recognized uses is in public health, where its potent disinfecting power is used to sanitize drinking water and swimming pools. This application ensures the elimination of harmful bacteria and other microorganisms.
Beyond disinfection, chlorine is a foundational building block in the production of countless materials. It is a precursor chemical used in the synthesis of many organic compounds, including solvents and pharmaceuticals. A substantial portion of industrial chlorine is also used in the manufacturing of plastics, most notably polyvinyl chloride (PVC), a common material in construction and consumer goods.