What are the physical states of halogens at room temperature?

At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids.

Halogens are a group of elements in the periodic table that include fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements are known for their high reactivity and their ability to gain an electron to achieve a stable electron configuration. The physical state of these elements at room temperature varies due to the differences in their atomic structures and intermolecular forces.

Fluorine and chlorine are gases at room temperature. Fluorine is a pale yellow gas, while chlorine is a greenish-yellow gas. These elements exist as diatomic molecules (F2 and Cl2), held together by relatively weak Van der Waals forces. The weak intermolecular forces mean that less energy is required to separate the molecules, hence they exist as gases at room temperature. To understand more about these forces, see the notes on Van der Waals forces.

Bromine is unique among the halogens as it is the only one that is a liquid at room temperature. It is a reddish-brown liquid that gives off a similarly coloured vapour. The stronger intermolecular forces in bromine, compared to fluorine and chlorine, mean that more energy is required to separate the molecules, hence it exists as a liquid.

Iodine and astatine are solids at room temperature. Iodine is a shiny, dark grey solid that sublimes to a purple vapour when heated. Astatine is a radioactive element and is usually produced in minute amounts for research purposes. It is believed to be a black or dark-coloured solid. The intermolecular forces in iodine and astatine are stronger than in the other halogens, hence more energy is required to separate the molecules, and they exist as solids. For further exploration of iodine's properties within its group, you might find the section on s, p, d, f blocks useful.

In summary, the physical states of the halogens at room temperature are determined by the strength of their intermolecular forces. The weaker the forces, the lower the temperature at which the substance will change from a solid to a liquid or a liquid to a gas. Additional information on the halogens, particularly their role in organic chemistry, can be explored in our notes on halogenoalkanes.