Elements are systematically organized on the periodic table. This arrangement groups elements by characteristics, leading to classifications like metals, non-metals, and metalloids. The question of how many metals exist is not as straightforward as simply counting, as the classification of certain elements presents a nuanced challenge.
Defining Metallic Properties
Metals possess a distinct set of physical and chemical characteristics. Physically, they exhibit a shiny appearance, known as luster, and are good conductors of both electricity and heat. Most metals are solid at room temperature, with mercury being a notable exception as a liquid. Metals are also known for their malleability, meaning they can be hammered into thin sheets, and ductility, allowing them to be drawn into wires.
Chemically, metals tend to lose electrons during reactions, forming positively charged ions called cations. This electropositive nature is linked to their relatively low ionization energies. Their ability to readily donate electrons contributes to metallic bonds, where a “sea” of delocalized electrons surrounds positive metal ions. This bonding structure accounts for many of their characteristic properties.
The Metal Count on the Periodic Table
Metals predominantly occupy the left and central portions of the table. Non-metals are found on the upper right side, while metalloids are situated along a diagonal line, often described as a “staircase,” separating the metals and non-metals. This line typically begins below boron and extends towards polonium.
Currently, out of the 118 known elements, approximately 90 to 95 are classified as metals. The exact number can vary slightly due to the ambiguous nature of metalloids. Metalloids exhibit properties intermediate between those of metals and non-metals. Examples include:
Boron
Silicon
Germanium
Arsenic
Antimony
Tellurium
They may have a metallic appearance but can be brittle and are only fair conductors of electricity, making their classification sometimes debated.
Diverse Classes of Metals
Alkali and Alkaline Earth Metals
Alkali metals, found in Group 1, are highly reactive, soft, silvery metals with low melting points and densities. They readily lose their single outer electron, forming +1 ions. Alkaline earth metals, in Group 2, are also reactive, silvery-white, and have two valence electrons, forming +2 ions.
Transition Metals
Transition metals, located in the d-block (Groups 3-12), are characterized by partially filled d-orbitals, leading to variable oxidation states and the formation of colored compounds. They are hard, strong, and have high melting points, boiling points, and densities.
Post-Transition Metals
Post-transition metals, found to the right of transition metals, include elements like aluminum, tin, and lead. These metals are softer, less dense, and have lower melting points compared to transition metals, often forming covalent bonds.
Lanthanides and Actinides
The lanthanides and actinides, often presented as two rows below the main body of the periodic table, are also metallic. Lanthanides are soft, silvery metals with high melting points and unique magnetic properties. They are electropositive and commonly exhibit a stable +3 oxidation state. All actinides are radioactive heavy metals, highly electropositive, and dense. They can tarnish readily in air and often form multiple oxidation states.
The Evolving Number of Metals
The total count of metals on the periodic table is not entirely static due to ongoing scientific discoveries. New, superheavy elements are continuously synthesized in laboratories, extending the periodic table beyond naturally occurring elements. These elements, with atomic numbers greater than 103, are often highly unstable and exist for very short durations.
The classification of these newly created elements as metals can be challenging and sometimes subject to debate. Their chemical properties are often predicted based on theoretical models and relativistic effects, which can significantly alter expected trends. As research progresses and more superheavy elements are synthesized and characterized, the precise number of elements recognized as metals may continue to subtly evolve.