We call the elements in the blocks of periods 4-7 and groups 3-12 the arsenic is a metalloid, and it has electron shells and valence electrons.

The elements in the blocks of period 4-7 and group 3-12 in the periodic table are in the d-block and d-block elements  are known as transition metals or transition elements.
Arsenic is a metalloid and it has four electron shells and five valence electrons.
the s and p orbital of Arsenic have 2 and 3 electrons respectively and which makes five valence electrons.