> It's true that it's less dense, but "float" is a huge understatement. That is, it skitters, like water on a hot frying pan.

No, if you wrapped it in some impermeable coating so it couldn't react with water it would still float.

> But, I guess because it's less dense, it doesn't detonate as often as sodium or potassium do.

It doesn't "detonate as often" because it is less reactive than sodium and potassium because it is less likely to lose it's outer electron because that outer electron is closer to the nucleus.

That also means it is denser.

Lithium is denser then sodium?

OK, sure. But TFA doesn't mention any coating.

I found a resource that corroborates what I said about behavior on water.[0] But it doesn't get into why that is.

And about density and electronegativity:

        g/cm^3   χ (Pauling)  1st ionization energy (kJ/mol)
   Li   0.535    0.98         520
   Na   0.968    0.93         496
   K    0.856    0.84         419

The difference in density is larger than that for electronegativity and 1st ionization energy. But yes, all three arguably play a role. Still, for Li vs Na, density seems like the major factor.

0) https://www.reference.com/science/alkali-metals-react-water-...

My high school chemistry teacher lamented that he had fond memories of taking a lump of a metal (sodium, potassium) and watching the fireworks with his students when they threw it in a pond out back. These days, he has to settle for taking a small sliver and dropping it into a beaker of water behind a safety shield.

A big chunk can jump back out at you, along the original angle of incidence. And it can really fuck up the pond's chemistry. So I endorse not throwing big chunks of alkali metal in ponds.

Putting a small lump in a bucket outdoors using a rope-activated rig sounds pretty reasonable, though.

Sodium in hot concentrated nitric acid is very impressive. As you say, outside with a string-activated rig. Short term, it does kill vegetation. But long term, it's fertilizer.

My school teacher chucked a golf-ball-size lump of sodium into the school swimming pool, then declared a wish to see the face of the guy who tests the pH of the pool the next morning.

Ha! My chemistry teacher did the same! Killed all the fish in the pond one time, or so he said.