Strictly speaking, both actinium and lawrencium have been labeled as group 3 elements, but both elements are often included in any general discussion of the chemistry of the actinide elements.
Strictly speaking, both actinium and lawrencium have been labeled as group 3 elements, because they both have a single valence electron in the 6d shell. However, both elements are often included in any general discussion of the chemistry of the actinide elements.