Why does a leaf float on the water's surface, according to the atomic theory?

Question

Today my chemistry professor was zooming through his Powerpoint presentation.

In my notes, I have the example "A leaf floats on the water's surface", but I was unable to write the rest of the slide down before he moved on.

Why does a leaf float on the water's surface? I remember my teacher saying something about the water's molecules being closer together than the leaf's molecules, but I don't remember exactly what he said. Could you help me? I need to add it to my notes.

Answer 1

What he might be saying was surface tension. Imagine a container filled only with pure double-distilled water. according to the expansion of the atomic theory on the inter-molecular forces of attraction, the water molecules behave in a way that it pulls other water molecules to itself. in the middle and bottom of the cntainer, the water molecues attract other water molecules from all directions; the water molecules on the surface would only attract otehr molecules from the sides and from the bottom, freeing up the surface. that would mean that the water surface is actually a "film" that can support any object with a relatively big surface area, like a leaf; meaning, not only is the surface tension a factor, surface area of the floting object also is. Imagine a piece of uncrumpled paper that was let go in mid air; it floats downward. however, if you crumple that piece of paper into a ball, it just drops. it's the similar case.

Answer 2

Something to do with density?  Does your teacher has a website you can go to with a podcast of the lecture on it?  Mine did and it helped a lot.