Radon difluoride (RnF2) is a compound of radon, a noble gas. Radon reacts readily with fluorine to form a solid compound, but this decomposes on attempted vaporization and its exact composition is uncertain. Calculations suggest that it may be ionic, unlike all other known binary noble gas compounds. The usefulness of radon compounds is limited because of the radioactivity of radon. The longest-lived isotope, radon-222, has a half-life of only 3.82 days.