The variety of chemical elements is classified based on shared characteristics, bringing order to the periodic table. The vast majority of these elements fall into two primary categories: metals and nonmetals. Understanding this division is the first step toward appreciating the differences in how these substances look and behave.
Observable Physical Characteristics
Metals and nonmetals display different physical traits, starting with their surface appearance. Metals typically exhibit a high luster, meaning they are shiny and reflective, which is why materials like silver and gold are valued for jewelry. In contrast, nonmetals generally have a dull, non-lustrous surface, such as solid sulfur or carbon in the form of coal.
The mechanical properties of the two groups also differ significantly under physical stress. Metals are known for their malleability, allowing them to be hammered or pressed into thin sheets without shattering, exemplified by aluminum foil. They are also ductile, meaning they can be drawn out into long, thin wires, a property utilized extensively in copper wiring. Nonmetals, especially in their solid forms, are typically brittle and will fracture or crumble when a force is applied.
Most metals exist as solids at standard room temperature, with the notable exception of mercury, which is a liquid. Nonmetals, however, are found across all three states of matter, including gases like oxygen and nitrogen, liquids such as bromine, and various solids like phosphorus and iodine. Furthermore, metals generally possess a high density, meaning they pack a lot of mass into a small volume. Nonmetals tend to have a much lower density in comparison.
A defining difference lies in their interaction with heat and electricity. Metals are excellent conductors of both thermal energy and electric current, which is why they are used for cooking utensils and electrical wiring. Nonmetals act as poor conductors, effectively serving as insulators, which is why materials like rubber and plastic are used to shield metal wires.
The Dividing Line: Metalloids and Periodic Table Placement
The periodic table is arranged to represent the transition from metallic to nonmetallic character. Metals occupy the large left and central portions of the table, including the alkali metals, alkaline earth metals, and transition metals. Nonmetals are clustered in the upper right-hand corner, with hydrogen being the only exception positioned on the far left.
A distinct zig-zag line, often called the “staircase,” runs diagonally through the p-block, acting as a boundary between the two major classes. Elements that lie directly along this line are known as metalloids, or semimetals. These elements exhibit a mix of physical and chemical characteristics from both categories.
Metalloids do not conform neatly to the properties of either group; for instance, they may appear metallic and shiny but behave as a poor conductor of electricity. Their most significant application comes from their unique electrical conductivity, which can be precisely controlled under specific conditions. This property makes elements such as silicon and germanium indispensable as semiconductors in the electronics and computer chip industries. Other metalloids include boron, arsenic, antimony, and tellurium.
Chemical Behavior and Compound Formation
The fundamental distinction between metals and nonmetals is rooted in how their atoms interact with electrons during chemical reactions. Metals tend to have a relatively weak hold on their outermost electrons. When they react, metal atoms readily lose one or more electrons to achieve a stable configuration. This loss results in the formation of a positively charged ion, known as a cation.
Nonmetals, in contrast, have a strong tendency to attract electrons. When reacting with metals, nonmetal atoms gain the electrons that the metal atoms lose, resulting in the formation of a negatively charged ion, or an anion. The complete transfer of electrons from a metal to a nonmetal is the defining feature of ionic bonding. The resulting oppositely charged ions are held together by a strong electrostatic force, forming an ionic compound like sodium chloride (table salt).
When nonmetals react with other nonmetals, they typically share electrons rather than transferring them. This sharing allows both atoms to fill their outer shells and is the basis of covalent bonding. The nature of the chemical bond is determined by the inherent chemical tendencies of the metal and nonmetal elements involved.