You know those moments when random questions pop into your head?

The kind you can’t believe you’ve never thought of before, and the answers to which won’t really affect your life, but now that you’ve wondered you just have to know?

Like, for example, why is mercury the only element that is liquid at room temperature?

Most metal elements have to reach extremely high temperatures in order to melt, but mercury is liquid all the way down to -38°F.

The reason for this boils down to mercury’s outer electrons and the combination of factors that makes them bond poorly.

This weakens the pull between one atom and another, so as soon as mercury picks up even a modest amount of energy, the organization of a solid breaks down. THis allows the atoms to move around freely.

Basically, the bonds are so weak and have so little energy, it doesn’t take much movement to break them apart.

At the atomic level, energy=heat.

It’s neighbors on the periodic table, gold and thallium, melt at more than 1000 and 300 degrees Celsius respectively.

Although it’s unexpected, we have been able to use it to our advantage in thermometers, barometers, and measuring blood pressure.

Why are the bonds between mercury’s electrons so weak, though?

It’s down to its spot on the periodic table, where three important effects combine:

1. It’s outer electron shell is full, making it harder for electrons to escape.
2. It experiences “lanthanide contraction,” which happens when the electrons of the 4f subshell shell don’t shield electrons further out from the positive charge of the nucleus. This causes the outer electrons to be pulled inward, leading to a greater density.
3. Mercury’s outer electrons also experience a relativistic contraction, moving nearly as fast as the speed of light.

The combination of these three effects interferes with the bonding between mercury atoms. They also keep to themselves when heated to a gas, more akin to a noble gas than an elemental gas.

There are a couple more elements that could be liquid at room temperature, but their half-lives are too short to be able to really observe them.

The transuranic elements Copernicium and Flerovium have to be produced artificially.

So for now, Mercury is on its own.

Kind of cool for it, right?

If you think that’s impressive, check out this story about a “goldmine” of lithium that was found in the U.S. that could completely change the EV battery game.