Understanding Halogens and Their Physical States

Halogens are a group of chemical elements found in Group 17 of the periodic table. They include Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At), and Tennessine (Ts). These elements are highly reactive nonmetals.

The physical state of elements changes with temperature and pressure. At standard room temperature (usually considered around 20-25°C) and pressure, different halogens exist in different physical states due to variations in their intermolecular forces (specifically, van der Waals forces), which increase with increasing molecular size and number of electrons.

Physical States of Common Halogens at Room Temperature

Let's examine the physical state of the common halogens listed in the options:

• Fluorine (F₂): Fluorine is the lightest halogen. At room temperature, it exists as a pale yellow gas.
• Chlorine (Cl₂): Chlorine is heavier than fluorine. At room temperature, it exists as a greenish-yellow gas.
• Bromine (Br₂): Bromine is heavier than chlorine. At room temperature, it is a volatile reddish-brown liquid. It is the only nonmetal element that is a liquid at room temperature.
• Iodine (I₂): Iodine is heavier than bromine. At room temperature, it exists as a lustrous purple-black solid. Iodine sublimes readily, turning directly from a solid into a gas upon heating.

Based on these facts, we can see that Bromine is the only halogen among the given options that exists in a liquid state at room temperature.

Summary Table of Halogen States

Therefore, the halogen that exists in a liquid state at room temperature is Bromine.

Revision Table: Key Properties of Halogens

Additional Information: Trends in Halogen Properties

The halogens show clear trends in their physical properties as you move down the group:

• Boiling and Melting Points: These points increase as you go down the group from Fluorine to Iodine. This is because the size of the electron cloud increases, leading to stronger London dispersion forces (a type of van der Waals force) between the molecules. Stronger forces require more energy to overcome, resulting in higher boiling and melting points. This trend explains the change in state from gas (low BP/MP) to liquid (intermediate BP/MP) to solid (higher BP/MP).
• Physical State: The change in state from gas (F₂, Cl₂) to liquid (Br₂) to solid (I₂) at room temperature directly follows the increase in boiling and melting points. Room temperature is above the boiling points of F₂ and Cl₂, between the melting and boiling points of Br₂, and below the melting point of I₂.
• Reactivity: Halogen reactivity generally decreases down the group, with Fluorine being the most reactive and Iodine being the least reactive among the common halogens.

Understanding these trends helps predict the properties of other halogens like Astatine, which is expected to be a solid at room temperature and even less reactive than Iodine.