Iron is not actually in column 8 of the periodic table, it is in the column just right of the "A" column, also known as groups 8(also known as group VIIIB), or just 8. It has to be here not because of the amount of valence electrons that an element might have or the group number; but from the number of the full energy levels the element contains.

Iron, and this goes for other group 8 elements, has all seven energy levels full from 1s-4f but its differentiating attribute is from its outermost energy level being the d orbital: 3d6/4s2