The electrons which are distributed in the outermost shell of the atom are called valence electrons.
These valence electrons can form a chemical bond only if the outer shell remains unclosed.
Valence electrons in an Iodine atom:
The element Iodine is in the fifth period and belongs to the Alkali metals group (group 17).
The atomic number of Iodine is 53.
The electronic configuration of Iodine can be written as
The valence electrons are the sum of the electrons in the outermost shell, that is two electrons and five electrons which gives a total of seven valence electrons.
Therefore, the valence electron in an Iodine atom is 7.