A chemical element is a unique species of atom, fundamentally defined by the specific number of protons contained within its nucleus, a count known as its atomic number. These fundamental substances cannot be broken down into simpler components through standard chemical processes, serving as the basic building blocks for all matter in the universe. The organization of these elements into the periodic table is based on recurring patterns in their characteristics. Classifying the elements into broad groups like metals and nonmetals is a necessary step to predict and explain how they interact to form the vast array of compounds around us.
Properties and Placement of Metals
Metals make up the majority of known elements and are primarily located on the left side and in the center of the periodic table. They include the highly reactive Alkali Metals, the Alkaline Earth Metals, the Transition Metals, Lanthanides, and Actinides. This group is physically characterized by a distinctive metallic luster, appearing shiny when polished or freshly cut.
A defining physical property of metals is their excellent ability to conduct both heat and electricity, which stems from the presence of delocalized electrons moving freely throughout the atomic structure. Most metals are solid at room temperature, with the notable exception of mercury, which exists as a liquid. They also possess high density and high melting points.
Metals are generally malleable, meaning they can be hammered into thin sheets, and ductile, allowing them to be drawn into thin wires. The chemical behavior of metals is centered on their tendency to readily lose electrons from their outermost shell during a reaction. This loss results in the formation of positive ions, or cations.
Because metals have relatively low ionization energies, they require less energy to give up these electrons, driving their participation in chemical bonding. This electron-donating characteristic is why metals like iron and sodium are highly reactive in their pure forms. These mechanical properties, combined with their conductivity, make elements like copper and aluminum indispensable in construction and electrical wiring.
Properties and Placement of Nonmetals
Nonmetals occupy a much smaller area of the periodic table, generally clustered on the upper right side, separated from the metals by a diagonal dividing line. The exception is hydrogen, which is considered a nonmetal despite its position in the top-left corner. This group includes the reactive Halogens and the stable Noble Gases.
In contrast to metals, nonmetals are typically poor conductors of both heat and electricity. When they exist as solids, such as sulfur or carbon, nonmetals tend to be brittle and lack metallic shine. At room temperature, nonmetals display diversity in their physical state, existing as gases (like oxygen and nitrogen), one as a liquid (bromine), and others as solids.
The chemical reactivity of nonmetals is defined by their strong tendency to either gain or share electrons to achieve a stable outer shell configuration. Elements like oxygen and chlorine, which have high electronegativity, attract electrons from metals to form negative ions, known as anions. This electron-gaining behavior drives the formation of ionic compounds when nonmetals react with metals.
When nonmetals react with each other, they typically share electrons to form covalent bonds, creating molecules like carbon dioxide and water. The chemical contrast between metals losing electrons and nonmetals gaining or sharing them forms the basis for the majority of chemical reactions.
The Boundary: Metalloids
The elements that sit directly along the dividing line between the metals and nonmetals are called metalloids, sometimes referred to as semimetals. This group, which includes elements like boron, silicon, and germanium, displays a mix of properties from both categories. Metalloids often possess a metallic luster, but they are physically brittle, a characteristic associated with nonmetals.
A defining feature of metalloids is their intermediate electrical conductivity. They do not conduct electricity as well as metals but are better conductors than most nonmetals. This unique quality allows them to function as semiconductors, a property that can be precisely controlled by temperature or the addition of impurities.
This semiconducting ability is the reason metalloids like silicon are foundational components in modern electronics, including computer chips and solar cells. Their positioning on the periodic table reflects this intermediate nature, acting as a transitional bridge between the electron-donating metals and the electron-accepting nonmetals.