The molecule structure of water contains two atoms of hydrogen and one of oxygen, water turns to vapor what happens to molecule structure

Nothing happens; water is still H₂O, even if it turns into ice, or vapor. Although, the molecules still move around faster, just like a normal gas would.

the density(ratio between mass and volume as m/v) decreases from top to bottom in periodic table group as the size increases and nuclear charge decreases. but in periods density increases from left to right as atom size decreases and nuclear charge increases.