Why do halogens form diatomic molecules

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Reactivity

The halogens are distinctly non-metals. They are among the most electronegative and reactive elements. In the elementary state they are all present as diatomic molecules. The dissociation energy of the halogen molecules is relatively low and can therefore easily be overcome by supplying heat or exposure to light. The dissociation energy decreases from the chlorine to the iodine. Fluorine is particularly easy to split into atoms, as the non-binding electron pairs in the molecule are repelled due to the small bond distance.

The strength of the intermolecular van der Waals forces determines the state of aggregation as well as melting and boiling points. Under normal conditions, fluorine and chlorine are gases, bromine is liquid and iodine is solid, but has a relatively high vapor pressure and sublimates easily.

, and have a layer structure in the crystal with pronounced cleavage parallel to the layers.

Although chlorine has a greater electron affinity than fluorine, it is a weaker oxidizing agent than fluorine. This can be explained by the fact that the oxidizing capacity of a halogen can be broken down into three sub-steps and is thus determined by three energetic influences. The higher the total energy released, the stronger the oxidizing power. The dissociation energy of to be applied is relatively small, whereas the hydration energy of the small fluoride ion is large. As a result, the oxidation process for fluorine is more exothermic than for chlorine.

The reactivity of the halogens decreases sharply from top to bottom within the group. The halogens react exothermically with metals and form salts (hence the name salt formers). This is how they occur in nature.