The halogens are Group 17 of the periodic table, running vertically from fluorine to astatine. This group of elements is highly reactive and includes an example of each phase of matter -- solid, liquid, and gas -- at standard temperature and pressure. The atoms of halogens contain seven valence electrons, making them eager to gain an electron and acquire a negative charge.
Chemical Reactivity of Halogen Atoms
Every atom is striving to achieve a complete set of eight electrons in its valence, or outer shell, as this is the most stable configuration. Halogen atoms contain seven electrons in the valence shell, making them easily prone to gaining an electron. Since they are close to obtaining a full octet of valence electrons, the halogens are very reactive elements.
The Effect of Atomic Radius
The smaller the atomic radius, the more influence the nucleus has on reactivity. Since the nucleus of an atom contains positively charged protons, it also attracts electrons. Halogen atoms already want to gain electrons, so the added force of nuclear pull makes them more reactive. The nucleus of smaller atoms is more exposed and thus exhibits a stronger pull. Therefore, the smaller the atomic radius, the more reactive the halogen atom, making fluorine the most reactive element in Group 17.
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