Helium is not a metal. Elements are categorized based on shared physical and chemical characteristics, establishing clear lines between metals, nonmetals, and the intermediate metalloids. Helium is classified as a nonmetal, belonging to the family of Noble Gases. Understanding this classification requires examining the defining properties of metals and nonmetals, and how helium’s atomic structure prevents metallic behavior.
Defining Metals and Nonmetals
Elements are divided into groups based on standardized physical and chemical properties. Metals typically possess a characteristic luster and are excellent conductors of both heat and electricity. They exhibit malleability (can be hammered into thin sheets) and ductility (can be drawn into wires). Chemically, metals tend to lose electrons during reactions, forming positively charged ions (cations).
In contrast, nonmetals display properties opposite to metals. They are generally poor conductors of heat and electricity. Solid nonmetals are typically brittle, not malleable or ductile. At standard temperature and pressure, nonmetals exist across all three states of matter, unlike most metals which are solid. Chemically, nonmetals tend to gain electrons, forming negatively charged ions (anions).
The Unique Properties of Helium
Helium fails to meet the criteria for a metal, beginning with its physical state. At standard temperature and pressure, helium exists as a colorless, odorless, tasteless, monatomic gas. This gaseous state contrasts sharply with the vast majority of metals, which are dense solids at room temperature. Its boiling point is the lowest of all known elements (approximately \(-268.9\) degrees Celsius), confirming its nonmetallic status.
Helium’s chemical profile provides the definitive reason for its nonmetallic classification. Helium atoms possess a full valence electron shell, containing two electrons in the outermost energy level. This complete shell configuration is exceptionally stable, making the atom chemically inert under normal conditions. It does not readily lose or gain electrons, which is the defining chemical behavior of metals and most other nonmetals, respectively.
The lack of free-moving electrons means helium is an electrical insulator and a poor conductor of electricity. Because it is a gas, helium is neither malleable nor ductile, as these properties are reserved for solids. The combination of its gaseous state, inertness, and inability to conduct electricity solidifies its identity as a nonmetal.
Helium’s Place on the Periodic Table
Helium is positioned in Group 18 of the periodic table, located on the far right side. This placement is significant because the periodic table groups elements with similar chemical behaviors, and the right side is where nonmetals are situated. The elements in Group 18 are known as the Noble Gases, defined by their characteristic chemical stability and low reactivity.
The physical organization of the periodic table represents the properties of the elements. Metals occupy the left side and the center, while nonmetals are found on the upper right side, separated by a diagonal line of metalloids. Helium is at the top of the nonmetal section. It is placed there because its full valence shell makes it the first and most stable of the Noble Gases.
Although helium is the second element by atomic number, its chemical properties dictate its position at the head of Group 18, rather than beside hydrogen. The full electron shell is the overriding factor for its placement, making it a nonmetal that forms virtually no chemical bonds. This location confirms its identity as a nonmetal, far removed from metallic elements characterized by their tendency to readily participate in chemical reactions.