Don't Mess With Mercury. Play With Gallium Instead!
Mercury is a mesmerizing element. Liquid at room temperature, yet dense enough that coins will float atop its surface, it has wowed a great many students in high school science classes over the decades.
Unfortunately, it is also incredibly toxic, releasing vapors that can acutely destabilize the central nervous system and, over time, damage the brain, kidney, and lungs, sparking symptoms like tremors, vision impairment, hearing impairment, speech impairment, as well as death.
Gallium closely mimics mercury's otherworldly appearance, though unfortunately lacks its prodigious density. But what gallium lacks in mass, it makes up for with other fascinating properties. Its melting point is roughly 85.7 degrees Fahrenheit, meaning it can be melted in the palm of one's hand, molded to form a shape, then quickly returned to solid form in a refrigerator. Gallium is also one of the few materials that expands when it solidifies, a trait only shared with water, silicon, germanium, antimony, bismuth, and plutonium.
Most interestingly, gallium ruthlessly attacks metals like aluminum, making for a fascinating demonstration. Place a little bit of gallium on an aluminum can, and the next day, the formerly sturdy can will crumble like ash.
You can also try this with a full clan, with potentially explosive results!
As the Royal Institution's Dan Plane explained, what you're seeing above is not a chemical process, but a physical one, called liquid metal embrittlement. Gallium atoms are actually squeezing in between the bonded crystal grains that comprise aluminum, thus making the grains far more apt to break apart.
At $317 per kilogram, gallium is roughly six times more expensive than mercury, so stocking the element might be a sizable ask for high school science departments whose budgets are already all-too-often imperiled. Still, for any teacher out there missing their mercury, requesting gallium is worth a shot!