Hydrogen occupies a distinct position on the periodic table. While placed in Group 1, typically associated with highly reactive alkali metals, hydrogen does not share their metallic characteristics. This apparent contradiction raises questions about its classification as a nonmetal. Understanding hydrogen’s fundamental atomic structure and chemical behavior clarifies why it is considered a nonmetal.
Hydrogen’s Unique Atomic Makeup
Hydrogen’s atomic structure is uniquely simple, consisting of a single proton in its nucleus and one electron in its outermost electron shell. This electron occupies the 1s orbital, which has a capacity to hold a maximum of two electrons. For hydrogen to achieve a stable electron configuration, similar to the noble gas helium, it needs to gain just one more electron to fill this shell.
This pursuit of a filled outer shell differentiates hydrogen from the alkali metals. Alkali metals also possess one valence electron, but their path to stability involves readily losing this electron to form a positive ion. In contrast, hydrogen’s single electron is held tightly by its nucleus due to its small size and the lack of inner electron shells to shield the nuclear charge.
The energy required to remove hydrogen’s single electron, known as its ionization energy, is notably high at 1312 kJ/mol. This is significantly greater than that of alkali metals; lithium, the alkali metal with the highest ionization energy, requires only 520 kJ/mol to lose its electron. This substantial energy requirement makes it energetically unfavorable for hydrogen to lose its electron and behave like a typical metal.
How Hydrogen Behaves Like a Nonmetal
Hydrogen’s atomic characteristics directly influence its nonmetallic chemical behavior. Instead of losing its electron, hydrogen typically achieves stability by forming covalent bonds, sharing its electron with another atom. This allows both atoms to attain a stable electron configuration, as seen in molecules like water (H2O), methane (CH4), and diatomic hydrogen (H2).
Typically, hydrogen exists naturally as a diatomic gas, H2. This gaseous state is a common characteristic among many nonmetallic elements, such as oxygen (O2) and nitrogen (N2), which also form diatomic molecules. Metals, by comparison, are typically solid at room temperature and do not exist as diatomic gases.
Hydrogen lacks the physical properties commonly associated with metals. It is not shiny, malleable (able to be hammered into sheets), or ductile (able to be drawn into wires). It is also a poor conductor of heat and electricity, unlike metals.
Hydrogen’s electronegativity, its ability to attract electrons in a chemical bond, is approximately 2.20 on the Pauling scale. This value is considerably higher than that of alkali metals, which have much lower electronegativity values (e.g., sodium is 0.93, lithium is 0.98). This higher electronegativity indicates hydrogen’s tendency to attract or share electrons, rather than readily losing them, confirming its nonmetal classification.