Liquid Elements

There are two elements that are liquid at the temperature technically designated 'room temperature' or 298 K (25°C) and a total of six elements that can be liquids at actual room temperatures and pressures.

Room temperature is a loosely defined term that can mean anywhere from 20°C to 29°C. For science, it's usually considered to be either 20°C or 25°C. At this temperature and ordinary pressure, only two elements are liquids:

• Bromine
• Mercury

Bromine (symbol Br and atomic number 35) is a reddish-brown liquid, with a melting point of 265.9 K. Mercury (symbol Hg and atomic number 80) is a toxic shiny silvery metal, with a melting point of 234.32 K.

When the temperature is slightly warmer, there are a few other elements found as liquids at normal pressure:

• Francium
• Cesium
• Gallium
• Rubidium

These four elements all melt at temperatures slightly higher than room temperature.

Francium (symbol Fr and atomic number 87), a radioactive and reactive metal, melts around 300 K. Francium is the most electropositive of all the elements. Although it's melting point is known, there is so little of this element in existence that it's unlikely you'll ever see a picture of this element in the liquid form.

Cesium (symbol Cs and atomic number 55), a soft metal that violently reacts with water, melts at 301.59 K. The low melting point and softness of francium and cesium are a consequence of the size of their atoms. In fact, cesium atoms are larger than those of any other element.

Gallium (symbol Ga and atomic number 31), a grayish metal, melts at 303.3 K. Gallium can be melted by body temperature, as in a gloved hand. This element displays low toxicity, so it's available online and may be used safely for science experiments. In addition to melting it in your hand, it can be substituted for mercury in the "beating heart" experiment and can be used to make spoons that vanish when used to stir hot liquids.

Rubidium (symbol Rb and atomic number 37) is a soft, silvery-white reactive metal, with a melting point of 312.46 K. Rubidium spontaneously ignites to form rubidium oxide. Like cesium, rubidium reacts violently with water.

That state of matter of an element may be predicted based on its phase diagram. While temperature is an easily controlled factor, manipulating pressure is another way to cause a phase change. When pressure is controlled, other pure elements may be found at room temperature. An example is the halogen element chlorine.