The small packets of silica you might find in a package of chips or an online order — the ones enticingly sprawled with “DO NOT EAT” — contain a fascinating bit of chemistry, as the silica within is just silicon dioxide, basically the same stuff as sand or glass. However, under an electron microscope, the silica gel bead reveals its amazing secret with a surface covered in tiny canyons 2.5 nanometers across. While glass has a density of 2,500 kilograms per cubic meter and quartz has a density of 2,650 kilograms per cubic meter, silica gel has just 700 kilograms per cubic meter because it is full of voids and has way more surface area than the little sphereule might imply. A gram of silica gel might have an internal surface area of up to 800 square meters (that’s two basketball courts), which allows it to condense 40 percent of its weight in water in those pores.
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