Solid: Protons

Introduction: It may seem something of a truism to describe an element as unique, but hydrogen is certainly one of the more unusual elements in the periodic table. It is the lightest element and consists of only a proton and an electron and is thus the only element not to contain a neutron in its main isotope (1H). In its stable molecular form (H2), it is also the least dense and the most abundant in the universe. Perhaps surprisingly, given that its low density results in gaseous hydrogen being almost nonexistent in the Earth’s lower atmosphere, it is also the...