The question of whether metals are mostly solid can be answered with a definitive yes, as nearly all metallic elements exist in a solid state at standard room temperature and pressure. A metal is fundamentally an element that readily forms positive ions and possesses metallic bonds, which allow it to be a good conductor of heat and electricity. The vast majority of metals exhibit the characteristic hardness and structural integrity that define the solid state.
The Defining Feature: Metallic Bonding
The solid nature of most metals is a direct consequence of metallic bonding. This bond is unlike covalent or ionic bonds, as it does not involve the sharing or complete transfer of specific electrons between two individual atoms. Instead, a metallic solid consists of a highly ordered, three-dimensional array of positively charged metal ions, or cations.
The outer-shell valence electrons detach from their parent atoms and become delocalized, shared collectively across the entire structure. This creates a mobile “sea of electrons” that flows freely around the lattice of positive metal ions. The structural integrity of the metal is maintained by the strong electrostatic attraction between these positive ions and the surrounding negative electron sea.
This powerful attractive force requires a significant amount of energy to overcome, which is why metals form a rigid, stable crystal lattice structure. The number of valence electrons contributed to the sea, and the size of the resulting cation, influence the overall strength of the bond and the physical properties of the metal.
Physical Characteristics of Metals
The robust nature of metallic bonding translates directly into the observable physical characteristics of solid metals. Due to the substantial energy required to break the strong electrostatic forces, most metals exhibit high melting and boiling points. For instance, iron melts at approximately 1,538 degrees Celsius, and tungsten requires 3,422 degrees Celsius to liquefy.
The closely packed atomic structure and strong inter-atomic forces also result in high density for many metals. The electron sea provides metals with their characteristic malleability and ductility, allowing the solid state to be worked.
When a force is applied, the layers of positive ions can slide past one another without fracturing the material, because the electron sea acts as a flexible, cushioning medium. The delocalized electrons reform the bonds in the new position, maintaining the overall cohesive force. This allows metals to be hammered into thin sheets (malleability) and drawn out into thin wires (ductility).
Notable Exceptions to the Rule
A small number of elements stand out as exceptions to the rule that metals are solid. The most widely known example is mercury (Hg), the only metal that is a stable liquid at standard room temperature, melting at -38.83 degrees Celsius. This unusual behavior is attributed to a unique electronic configuration that results in weaker inter-atomic forces than are typical for metals.
Several other metals have melting points near or just above room temperature. Gallium (Ga) melts at approximately 29.76 degrees Celsius, easily turning into a liquid when held in the warmth of a human hand. Similarly, cesium (Cs) has a melting point of 28.5 degrees Celsius, making it a liquid on a warm day.
These elements have a less efficient packing arrangement in their solid lattice structure compared to most metals. This structural difference, combined with specific electron shell effects, results in a reduced energy requirement to transition from a solid to a liquid state.