Why is Chlorine a Halogen? (+ 3 More Things to Know)

Yes, chlorine is a halogen. Chlorine is a halogen because it belongs to Group 17 (Group VIIA) of the periodic table, which is known as the halogen group. ¹ Halogens are called so because they are salt-forming elements, and chlorine exhibits this property by readily forming chloride salts.

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Explanation: Why is chlorine a halogen?

Chlorine is classified as a halogen because it possesses similar chemical properties to other elements in its group, namely fluorine, bromine, iodine, and astatine. The term “halogen” originates from the Greek words “halos” meaning “salt” and “genes” meaning “forming” or “generating.” Halogens are called so because they readily form salts when they react with metals. ²

Chlorine exhibits this property by readily forming chloride salts. Chlorine atoms have seven electrons in their outermost energy level, one electron short of a stable configuration.

This electron deficiency makes chlorine highly reactive and eager to gain one electron to achieve a stable electron configuration. As a result, chlorine can readily react with metals, such as sodium, to form ionic compounds known as chloride salts. ³

For example, when chlorine reacts with sodium, it accepts one electron from sodium, forming an ionic bond and resulting in the formation of sodium chloride (NaCl), which is commonly known as table salt. ⁴ This process of electron transfer from the metal to the halogen is characteristic of the reactivity of halogens, including chlorine.

In summary, chlorine is considered a halogen because it belongs to a group of elements that readily form salts when they react with metals. Chlorine’s ability to readily form chloride salts is a key characteristic of halogens, which are known as “salt-forming elements.” ⁵

Properties of chlorine that classify it as a halogen

Chlorine possesses several properties that classify it as a halogen. Here are some key properties of chlorine that align with the characteristics of halogens:

• Electronic Configuration: Chlorine belongs to Group 17 (Group VIIA) of the periodic table, known as the halogens. It has an electronic configuration of 1s² 2s² 2p⁶ 3s² 3p⁵, with seven valence electrons in its outermost energy level. ⁶
• Reactivity: Like other halogens, chlorine is highly reactive due to its electronic configuration. It only requires one additional electron to achieve a stable electron configuration of the previous noble gas, argon (1s² 2s² 2p⁶ 3s² 3p⁶). This electron deficiency makes chlorine eager to gain one electron, leading to its strong reactivity.
• Electronegativity: Chlorine has a high electronegativity value, indicating its ability to attract electrons towards itself when forming chemical bonds. This property is characteristic of halogens, as they tend to gain electrons and form negative ions (anions) during chemical reactions.
• Oxidizing Agent: Chlorine is a powerful oxidizing agent, capable of accepting electrons from other elements or compounds. It readily undergoes reduction (gains electrons) while oxidizing other substances. This property is a common feature of halogens and is utilized in various chemical reactions and disinfection processes.
• Salt Formation: As mentioned earlier, halogens are called “salt-forming elements” due to their ability to readily react with metals and form ionic compounds known as halide salts. Chlorine readily forms chloride salts when it reacts with metals like sodium, potassium, or calcium.
• Physical State: Chlorine is a greenish-yellow gas at room temperature and standard pressure. ⁷ This gaseous state is a common characteristic of halogens. However, chlorine can also exist in liquid and solid forms under certain conditions.

These properties collectively classify chlorine as a halogen and align it with the other elements in the halogen group, such as fluorine, bromine, iodine, and astatine.

How is chlorine different from other halogens?

While chlorine shares many similarities with other halogens, it also exhibits some distinct differences. Here are a few ways in which chlorine differs from other halogens:

• Physical State: Chlorine is the only halogen that is a gas at standard temperature and pressure. ⁸ Fluorine is also a gas, but it is much more reactive and typically handled in a condensed form. Bromine is a reddish-brown liquid, iodine is a solid with a purple color, and astatine is a rare radioactive element that exists as a solid or vapor.
• Chemical Reactivity: Chlorine is less reactive than fluorine but more reactive than bromine, iodine, and astatine. This reactivity trend generally follows the order of the halogen group, with fluorine being the most reactive and astatine being the least reactive. ⁹ Chlorine’s reactivity is still notable, as it readily reacts with a wide range of substances, including metals, organic compounds, and other non-metals.
• Biological Importance: Chlorine differs significantly from other halogens in terms of biological roles. While chlorine is widely used for disinfection and water treatment due to its antimicrobial properties, it is not an essential element for living organisms. ¹⁰ In contrast, iodine is essential for the synthesis of thyroid hormones in humans, and fluorine is found in the structure of certain biologically active compounds like fluorapatite in teeth and bones. ¹¹
• Industrial Applications: Chlorine has a wide range of industrial applications due to its reactivity and ability to form compounds. It is used in the production of various chemicals, including plastics, solvents, disinfectants, and bleach. ¹² Other halogens also find industrial applications, but chlorine is the most extensively utilized halogen in terms of commercial applications.
• Environmental Impact: Chlorine, when released into the environment in large quantities, can have adverse effects. It is a toxic gas that can harm human health and the environment. In contrast, other halogens like fluorine and iodine have less significant environmental impacts, while bromine and astatine have limited industrial use and are relatively less studied in terms of their environmental effects.

While chlorine shares common properties with other halogens, these differences highlight its unique characteristics and applications compared to the rest of the halogen group.

Further reading

Why is Iodine a Halogen?
Why are Halogens So Reactive?
Does water conduct electricity?
Why is Cobalt Magnetic?
Is Aluminum Magnetic? 

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