How does helium differ from the elements in its group?

Helium only have 2 electrons in its valence shell. On the other hand the elements in its group have 8 electrons in its valence shell. So the difference is the amount of electrons each has.

Helium only has 2 electrons in its outermost shell (valence shell), while the other elements in its group (called the noble gases) have 8 electrons in their outermost shell (valence shell.)