The chemical element with the lowest density is hydrogen, which has a density of 0.00008988 grams per cubic centimeter. Hydrogen is also the smallest and simplest element and generally comprises one proton, one electron and no neutrons.
The next elements with the lowest density are helium, neon, nitrogen, oxygen and fluorine, all of which are gases. In fact, the first 11 elements with the lowest density are all gases. Lithium is the least dense solid element, with a density of 0.534 grams per cubic centimeter, which makes it only about half as dense as water. The most dense naturally occurring elements are iridium and osmium.