Overview
State is not an intrinsic label valid under every condition. A substance can be solid, liquid or gas depending on temperature and pressure, so a periodic table should always make its reference conditions clear.
How to use this idea
Why an element’s physical state depends on temperature and pressure.
Even a familiar label hides an experimental condition
We casually call oxygen a gas and iron a solid, but neither statement is complete without conditions. Cool oxygen enough and it becomes a liquid; heat iron enough and it melts. Phase is a property of matter under a specified temperature and pressure, not a permanent badge attached to an element.
This becomes especially important at the far end of the table. For atoms made only a few at a time, nobody can simply place a visible sample in a flask. Some familiar-looking properties on superheavy-element charts are predictions, and a careful reference should say so.
State depends on conditions
Labels such as solid, liquid and gas are meaningful only when temperature and pressure are specified. At ordinary laboratory conditions most elements are solids, bromine and mercury are liquids, and a limited set are gases. Near a phase transition, however, the classification can change with only a modest change in temperature.
For superheavy elements, experimentally established bulk phase behaviour may be unavailable because only very small numbers of atoms have been produced. In those cases Mendeleev.com should distinguish measured facts from theoretical predictions.