Elements such as fluorine, chlorine, bromine, iodine, and astatine belong to Group 7, Halogens. At room temperature, fluorine is a yellow gas, chlorine is a pale green gas, bromine is a red liquid, and iodine is a purple solid. Astatine is a radioactive element, therefore it exists only in small amounts. All the halogens exist in diatomic molecules. They have high ionization energies and are the most electronegative elements. Their electron configuration ns2 np5 make them perfect elements in order to react with Group 1 and 2 metals since they want an electron which Group 1 and 2 are willing to give. Therefore, out of all the main group elements, Halogens react vigorously with Group 1 and Group 2 metals. All the alkali metals react vigorously with halogens to produce salts, most important NaCl and KCl. Sodium Chloride is used as a preservative for meat and to melt the ice on the roads. KCl is important for plant fertilizers since potassium helps plant growth. The metal halides form white ionic crystalline solids. They are all soluble in water except LiF because of a high lattice enthalpy due to the electrostatic attraction between Li+ and F- ions.
All halogens are quite reactive, and in the natural world they always occur combined with other elements. Fluorine reacts so readily with almost any substance it contacts that chemists were not successful in isolating pure fluorine until. Chlorine, bromine, and iodine are progressively less reactive but still form compounds with most other elements, especially metals. Iodine combines less vigorously with alkali metals than other halogens, but its reactions are analogous to the reactions of alkali metals with fluorine, chlorine and bromine. Compounds of an alkali metal and a halogen, such as sodium chloride, potassium fluoride, lithium bromide, or caesium iodide, have closely related properties. They belong to a general category called salts, all of whose members are similar to ordinary
References: DENNISTON, K. J. (2010). General, Organic and Biochemistry: 7th Revised edition. London, McGraw Hill Higher Education. HILL, G. C., & HOLMAN, J. S. (2000). Chemistry in context. Walton-on-Thames, Nelson. SMITH, M. (2012). OCR(A) AS chemistry. Unit F321, Atoms, bonds and groups. Deddington, Philip Allan Updates