Of all the 118 elements in the periodic table, many are solids at room temperature. While a number are gases, are only two elements are liquid at room temperature. These two are mercury and bromine.
Mercury with a melting point of minus 38.83 C (234.32 K, minus 7.89 F) and a boiling point of 356.73C (629.88 K, 674.11 F) is the most well known of these. Also known as quicksilver, mercury fills many a thermometer. Named after the planet and the Roman god Mercury, its symbol Hg comes from the Greek “hydrargyrum” meaning liquid silver. The atomic number of mercury, 80, puts the element in Group 12, Period 6 of the periodic table.
Mercury has numerous common uses. In addition to its use in thermometers, barometers and other scientific instruments, mercury extends the life of dry cell batteries. Its vapor is used in some fluorescent tubes as such it is seen in street lighting and illuminated advertisements.
Bromine (atomic number 35), a halogen found in Group 17, Period 4 of the periodic table, has a melting point of minus 7.2 C (265.95 K, 19.0 F) and boiling point of 58.8 C (331.95 K, 137.8 F). It is a brown smelly liquid and its name reflects this as it derives from the Greek word for stench “bromos”. It is toxic burning skin on contact and in vapor form irritating the nose, throat and eyes. While the pure element has little usage, silver bromide is valuable in photography. Before the introduction of unleaded petroleum ethylene dibromide, added to engines, prevented lead accumulation.
Although no other elements are liquid at room temperature, there are four others with melting points just above normal room temperature. The most common of these is the bright silver colored metal gallium (atomic number 31). This element, found in Group 13, Period 4 of the periodic table, has a melting point of 29.76 C (302.91 K, 85.57 F) and a boiling point of 2204 C (2477 K, 3999 F). This element’s large liquid range makes it ideal for use in high temperature thermometers. It is also used to form low-melting point alloys with a variety of metals.
The other three elements are all alkali metals belonging to Group 1 of the periodic table. None of these is particularly common. Francium, a radioactive element with atomic number 87, is so rare that scientists estimate only one ounce of it exists on earth at any time! Its longest-lived isotope with a half-life of only 22 minutes is francium-223. Francium’s melting point is 27 C (300 K, 81 F) and its boiling point 677 C (950 K, 1250F).
The other two low melting point alkali metals are both highly reactive requiring storage under mineral oil to prevent them reacting with air. The first is rubidium (atomic number 37)with a melting point of 39.31 C (312.46 K, 102.76 F) and a boiling point of 688 C (961 K, 1270°F). The final element is cesium (atomic number 55) with a melting point of 28.44 C (301.59 K, 83.19 F) and a boiling point of 671 C (944 K or 1240 F). Vacuum tube technology uses both of these elements as “getters” to remove trace gases from the tubes. Atomic clocks are based on cesium.