An element is a pure chemical substance made up of only one type of atom. Matter exists in three common states—solid, liquid, or gas—and an element’s state depends on its temperature and pressure. While scientists use Standard Temperature and Pressure (STP) (\(0^\circ\text{C}\) and \(1\text{ atm}\)), “room temperature” is generally understood to be a warmer range, often between \(20^\circ\text{C}\) and \(25^\circ\text{C}\) (\(68^\circ\text{F}\) and \(77^\circ\text{F}\)). Most elements are solid at this ambient temperature, but a few possess melting points low enough to remain liquid indoors.
The Two Elements Liquid at Standard Conditions
Only two elements are liquids at standard room temperature: the metal Mercury (\(\text{Hg}\)) and the nonmetal Bromine (\(\text{Br}\)).
Mercury is a silvery, dense metal with a low melting point of \(-38.83^\circ\text{C}\) (\(-37.89^\circ\text{F}\)), keeping it fluid under normal conditions. This property made it useful in thermometers and barometers, though its toxicity has led to a reduction in its use.
Bromine is the only nonmetallic element that is liquid at room temperature, appearing as a volatile, reddish-brown fluid. It is a halogen with a melting point of \(-7.2^\circ\text{C}\) (\(19^\circ\text{F}\)). Due to its strong odor and high reactivity, it has applications in disinfectants, agricultural chemicals, and flame retardants.
Elements That Melt Just Above Room Temperature
A small group of elements are solid at \(25^\circ\text{C}\) but transition into a liquid state with only a slight increase in temperature. These elements possess melting points just above typical room temperature, making them liquids in warmer environments or when handled.
Gallium (\(\text{Ga}\)) is the most prominent example, melting at approximately \(29.8^\circ\text{C}\) (\(85.6^\circ\text{F}\)). A piece of solid Gallium will quickly liquefy if held in a person’s hand, as average human body temperature is around \(37^\circ\text{C}\). Gallium is a soft, bluish-silver metal used in semiconductor manufacturing, particularly in compounds like gallium arsenide for LEDs and integrated circuits.
Cesium (\(\text{Cs}\)) and Rubidium (\(\text{Rb}\)) also melt at temperatures slightly higher than room temperature, near \(28.5^\circ\text{C}\) and \(39.3^\circ\text{C}\) respectively. These highly reactive alkali metals show how minor temperature fluctuations can shift an element’s physical state.
Factors Governing an Element’s State of Matter
The state of matter an element adopts is determined by the balance between the kinetic energy of its atoms and the strength of the forces holding them together. The melting point is the temperature at which thermal energy overcomes these interatomic forces, causing the solid structure to collapse into a liquid state. Elements liquid at room temperature have weak attractive forces that require minimal energy to break.
Mercury’s Weak Metallic Bonds
The weakness of metallic bonding in Mercury is attributed to its full electron shells and relativistic effects. These effects pull Mercury’s electrons closer to the nucleus, making them less available to form the strong metallic bonds seen in most other solid metals.
Bromine’s Molecular Structure
Bromine’s liquid state is due to its molecular structure, where two Bromine atoms form a diatomic molecule (\(\text{Br}_2\)) held by a strong covalent bond. However, the separate \(\text{Br}_2\) molecules are only attracted to each other by weak London dispersion forces, which are easily overcome by thermal energy at room temperature. This difference in fundamental forces explains why elements like Gallium liquefy easily, while elements with strong covalent networks, such as Tungsten, require thousands of degrees to melt.