Question

How do we determine the reactivity of halogen elements?

Answer 1

Hint: The group of halogens is the only group in the periodic table which contains elements in all three familiar states of matter at standard temperature and pressure. Fluorine is known to be pale yellow gas. Chlorine is known to be greenish gas. Bromine is known to be a dark red liquid. Iodine is a black solid and when heated it forms a purple vapour . Astatine is a black solid.

Complete answer:
The reactivity of elements in Group 7 decreases as they move down the group. When non-metal atoms react with metals, they gain electrons. A halogen atom gets one electron into its highest occupied energy level (outer shell) when it reacts, resulting in a single negative charged ion.
As we move through the group, one extra electron shell is added, increasing the atom's atomic radii. As we move down the group, the electrons in the outer shell migrate further away from the nucleus, and the attraction force between the electrons and the nucleus weakens.
The larger atoms have a weaker pull, making it more difficult to gain an electron. As a result, the atom's capacity to attract electrons to fill the outermost shell decreases, lowering the atom's reactiveness.

Note:
Halogens are strongly electronegative due to their large effective nuclear charge. As a result, they are very reactive and can gain an electron through chemical reactions. In significant levels, halogens can be toxic or deadly to living beings.