Answer 1:
I am first going to guess that when you say
floating, you mean in water. There are very few
elements that float in water. To float in
water, their density would have to be less than
the density of water. Something that has higher
density has more stuff packed into a small space.
Something with lower density has less stuff packed
into that same space. For example, a chunk of
metal the size of a brick will have much higher
density than a chunk of Styrofoam the same size.
So to see if something can float in water, you
can compare the density of it to the density of
water. I found a great periodic table
click here that has the density of each
element in the top right corner.
Going in order, we can see that hydrogen and
helium both have densities less than water,
which would be 1.0 g/mL. Those are gases, and so
you can imagine a gas bubble floating to the
surface and escaping, just like carbon dioxide
does in bubbly soda. The next one that we see is
lithium. Lithium is definitely a lower density
than water. So is sodium (element
symbol Na) below it and potassium (element symbol
K)! Unfortunately, all three of those elements are
really reactive with water, to the point that if
you drop a small amount in, it can be like a small
explosion!
Some other elements that would float in
water would include nitrogen, oxygen, fluorine,
neon, chlorine, and argon. (On the chart, it
says that argon has a density of 1.784, but this
is in g/L. Water has a density of 1.0 g/mL which
is equal to 1000 g/L. So argon is definitely less
dense than water!)
All of those elements are gases. So they would
float, but you would have to put them into the
water as bubbles. If you meant to ask what
elements would float in air, the density of air is
about 1.2 g/L. You might have seen a helium
balloon take off into the air when you let it go,
so you know that helium can float in air. Hydrogen
can, too. And according to that chart, it looks
like neon would also float in air. Hope
that helps!
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