Atoms of elements in the same group of the periodic table share similar chemical properties and have the same number of valence electrons.
The atomic radius of atoms increases from top to bottom in a Group because you are adding one more electron shell at each step.
Atomic mass increases from top to bottom because there are more protons and neutrons in the nucleus.
For metals, reactivity also increases from top to bottom because the valence electrons are further from the nucleus. Other elements can attack the valence electrons more easily.
For nonmetals, reactivity increases from bottom to top in a Group because the valence electrons are closer to the nucleus, which then has a greater attraction for extra electrons.
