Periodic table: number of elements in solid, liquid or gas form at standard sate

Of the 118 known elements in the periodic table, only 14 are not found in a solid state at room temperature. Mercury (a metal) and bromine (a halogen) are the only elements found in liquid form at room temperature, while the seven noble gases, the nonmetals hydrogen, nitrogen, and oxygen, as well as the halogens fluorine and chlorine make up the 12 gaseous elements at room temperature. Simply speaking, the state of these substances at room temperature depends on how strong the attraction is between atoms or molecules, i.e. hydrogen molecules (H₂) have relatively weak interactions with one another and therefore have much lower melting and boiling points, and it is a gas at room temperature.

However, elements that are gaseous or liquid at room temperature may bond with other elements, and the change in composition can increase interaction between the molecules, lowering the melting or boiling point and causing a change in state. The most obvious example of this is when hydrogen and oxygen molecules bond to form water - it is a liquid at room temperature as the attraction between H₂O molecules is much higher than H₂ or O₂ alone.