 However, going down group 17, the metallicity of the elements increases; for example, iodine already exhibits a metallic luster in the solid state, and astatine is often classified as a metalloid due to its properties being quite far from those of the four previous halogens.As such, an extrapolation based on periodic trends would predict tennessine to be a rather volatile post-transition metal.Calculations have confirmed the accuracy of this simple extrapolation, although experimental verification of this is currently impossible as the half-lives of the known tennessine isotopes are too short.