The physical state of an element is determined by the balance between the kinetic energy of its atoms and the attractive forces holding them together. This balance is highly dependent on temperature, and a standard “room temperature” range is used, typically defined as 20°C to 25°C (68°F to 77°F). Under these standard ambient conditions, elements can be found in all three common states of matter: solid, liquid, and gas. The vast majority of the known elements exist as solids.
The Majority: Elements That Exist as Solids
The periodic table is overwhelmingly populated by elements that are solid at room temperature, accounting for approximately 94 of the 118 known elements. This majority includes all of the metals: the alkali metals, alkaline earth metals, transition metals, and the rest of the metallic elements. These metals are characterized by their strong metallic bonding, which locks their atoms into a fixed, rigid lattice structure. Examples include Iron, Gold, Copper, and Aluminum.
The metalloids, which possess properties of both metals and nonmetals, are also entirely solid at room temperature; this group includes Silicon and Boron. Additionally, several nonmetals are solids, exhibiting different types of atomic bonding. For instance, Carbon (in forms like diamond or graphite), Sulfur, Phosphorus, and Iodine are all nonmetallic solids found under standard conditions.
The physical nature of these elements as solids means their atoms are held in fixed positions, only able to vibrate in place. This limited movement results in a definite shape and volume for the element.
The Exceptions: Liquids and Gases at Room Temperature
While most elements are solids, a small number exist as liquids or gases at the standard room temperature range. Only two elements are liquids under these conditions: Mercury and Bromine. Mercury is a silvery metal, unique for having a melting point below room temperature, while Bromine is a reddish-brown nonmetal.
The remaining eleven elements are gases under standard conditions. This group includes all six noble gases (Helium, Neon, Argon, Krypton, Xenon, and Radon), which exist as single atoms. The other gaseous elements are nonmetals that form diatomic molecules, such as Hydrogen, Nitrogen, Oxygen, Fluorine, and Chlorine.
These elements are gases or liquids because the attractive forces between their atoms or molecules are weak enough to be overcome by the kinetic energy present at room temperature. For the gases, the particles are far apart and move independently, while for the liquids, the particles remain close but can move past one another.
What Makes an Element Solid
The physical state of an element is determined by the strength of the interatomic forces holding its atoms together relative to the thermal energy of the system. For an element to be a solid at room temperature, its constituent atoms must be bound by forces strong enough to hold them in a fixed, ordered arrangement called a crystal lattice. This strength is quantified by the element’s melting point; a high melting point indicates strong attractive forces that require substantial energy to break.
Metallic Bonding
In metals, the solid state is maintained by metallic bonds, which involve a lattice of positive ions surrounded by a “sea” of delocalized valence electrons. This strong, non-directional attraction creates a highly stable structure that accounts for the high melting points of most metals.
Nonmetallic Bonding
For nonmetallic solids, two main types of bonding maintain the solid state. Covalent-network solids, such as Carbon (diamond), hold atoms together by a network of strong, directional covalent bonds. The energy required to break these bonds results in some of the highest melting points in the periodic table. Other nonmetallic solids, such as Iodine, are molecular solids where individual molecules are held together by weaker intermolecular forces, specifically London dispersion forces, which are strong enough to maintain the solid state at room temperature.