Chlorine (Cl) is classified as a nonmetal, placing it outside the categories of metals and metalloids on the periodic table. This element exists as a diatomic molecule, Cl₂, appearing as a greenish-yellow gas with a distinct, pungent odor under standard temperature and pressure. Understanding this classification requires looking at the broader system used to organize all known elements.
How Elements Are Classified
Elements are grouped into three major categories—metals, metalloids, and nonmetals—based on their fundamental physical and chemical characteristics. Metals make up the majority of the periodic table. They are typically solid at room temperature, exhibit a high metallic luster, and are excellent conductors of both heat and electricity. Metals are also malleable and ductile, meaning they can be hammered into thin sheets or drawn into wires.
Nonmetals generally display the opposite set of characteristics in their elemental state. They are poor conductors, acting as insulators for heat and electricity, and lack the shiny appearance of metals. Nonmetals may exist as gases, liquids, or brittle solids at room temperature.
Metalloids occupy a narrow, diagonal region on the periodic table and possess properties intermediate between metals and nonmetals. These elements, such as silicon and arsenic, can sometimes conduct electricity, but not as efficiently as metals. This intermediate conductivity earns them the classification of semiconductors.
The Properties That Define Chlorine as a Nonmetal
The properties of Chlorine align with the definition of a nonmetal, justifying its classification. Unlike metals, which tend to be solids, elemental chlorine exists as a gas at standard temperature, liquefying only at a very low boiling point of approximately -34.04°C. The pale yellowish-green gas also lacks the characteristic sheen or luster associated with metals.
Chlorine is a poor conductor of heat and electricity, a characteristic property of nonmetallic elements. Chemically, the element is a strong oxidizing agent, meaning it readily accepts electrons from other atoms during reactions. This tendency to gain an electron is a defining feature of nonmetals, which seek to complete their outer valence shell.
The atomic structure of chlorine, with seven valence electrons, drives its high reactivity and electron affinity. By acquiring just one additional electron, chlorine achieves a stable, full outer shell. This is the driving force behind its behavior as a nonmetal. This drive to gain electrons contrasts sharply with metals, which tend to lose electrons to form positive ions.
Chlorine’s Place on the Periodic Table and Common Uses
Chlorine (atomic number 17) is located in Group 17 of the periodic table, a column known as the Halogens. This family includes fluorine, bromine, iodine, and astatine, all of which are nonmetals and share the property of having seven valence electrons. The Halogen family is known for its high reactivity because of its strong desire to acquire the single electron needed for stability.
The reactivity of chlorine allows it to form compounds with nearly every other element, contributing to its wide range of commercial applications. Chlorine is recognized for its use as a powerful disinfectant, employed in the purification of public drinking water supplies and the sanitation of swimming pools.
Beyond its role as a sanitizer, chlorine is a fundamental component in industrial chemistry and manufacturing. It is a necessary ingredient in the creation of numerous products, including the plastic polyvinyl chloride (PVC) used in pipes and construction materials. Chlorine also forms the negative ion in sodium chloride (NaCl), commonly known as table salt, which is essential for human diet and industrial processes.