Nonmetals are the elements that sit on the right side of the periodic table and lack the hallmark traits people associate with metals: they generally do not conduct electricity, are not shiny or malleable, and tend to gain electrons rather than lose them in chemical reactions. Roughly 18 elements qualify as nonmetals depending on where you draw the boundary with metalloids, yet this comparatively small group accounts for the overwhelming majority of the matter you encounter in everyday life, from the air you breathe to the water you drink to the molecules that make up your body.
How Nonmetals Look and Feel
The physical properties of nonmetals are best understood by contrast with metals. Metals are typically shiny, dense, solid at room temperature, and easy to bend or hammer into shape. Nonmetals break almost every one of those rules. Most are dull rather than lustrous, and in solid form they tend to be brittle: hit a chunk of sulfur with a hammer and it shatters rather than flattening out. Many nonmetals are gases at room temperature, including oxygen, nitrogen, fluorine, chlorine, and all six noble gases. Bromine is the only nonmetal that exists as a liquid under normal conditions. The solid nonmetals, such as carbon, sulfur, phosphorus, selenium, and iodine, are scattered across the periodic table and vary widely in appearance, from the deep yellow of sulfur crystals to the dark violet sheen of iodine.
Nonmetals also tend to have lower melting and boiling points than metals. Nitrogen, for instance, boils at about −196 °C, while oxygen boils at roughly −183 °C. Even solid nonmetals melt at far lower temperatures than most metals: sulfur melts around 115 °C, and phosphorus melts near 44 °C. The exceptions here are striking. Carbon in its diamond form does not melt under normal atmospheric pressure at all; it sublimes above 3,500 °C, which actually exceeds the melting point of iron. That kind of outlier is a recurring theme with nonmetals: the group is so diverse that almost every generalization has a notable exception.
Density is another area where nonmetals diverge from metals. Gaseous nonmetals are obviously far less dense than any metal, but even the solid nonmetals are lightweights compared to iron, copper, or gold. Sulfur has a density of about 2 grams per cubic centimeter, and phosphorus sits at roughly 1.8. Diamond, at around 3.5, is denser than most nonmetals but still lighter than aluminum oxide and far lighter than any transition metal.
Electrical and Thermal Conductivity
Poor conductivity is one of the most practically important physical traits of nonmetals. Metals conduct electricity because their outermost electrons are free to move through the material. In nonmetals, electrons are generally locked into covalent bonds or tightly held by the atom, so they do not flow in response to a voltage. This is why nonmetals serve as electrical insulators: rubber, plastic (long chains of carbon and hydrogen), glass (silicon and oxygen), and sulfur are all poor conductors, and that property is exactly what makes them useful for insulating wires, coating tools, and building electronics housings.
Thermal conductivity follows a similar pattern. Metals feel cold to the touch because they rapidly pull heat away from your skin. Nonmetals in solid form feel comparatively warm because they transfer heat slowly. Wood, which is mostly carbon, hydrogen, and oxygen arranged in cellulose, is a familiar example.
The glaring exception is graphite, one of carbon’s solid forms. In graphite, carbon atoms are arranged in flat sheets where each atom shares electrons with three neighbors, leaving one electron per atom free to move within the plane. This gives graphite respectable electrical conductivity along the sheets, enough to use it as an electrode material in batteries and industrial electrolysis. Across the sheets, graphite is a poor conductor, so its conductivity is directional. Diamond, by contrast, is an excellent thermal conductor but an electrical insulator because every one of carbon’s four outer electrons is locked into a bond with a neighboring carbon atom.
Why Carbon Alone Deserves Its Own Conversation
Carbon is the most structurally versatile element on the periodic table, and it bends nearly every rule you might try to set for nonmetals. Depending on how its atoms bond and arrange themselves, carbon can form the layered semiconductor graphite, the extraordinarily hard insulator diamond, high-surface-area amorphous carbons like charcoal and activated carbon, and nano-scale structures such as fullerenes and nanotubes.1Journal of Chemical Technology & Biotechnology. Carbon allotropes: beyond graphite and diamond That range of forms, called allotropy, means carbon can be softer than talc (in graphite) or harder than any other naturally occurring material (in diamond), can conduct electricity or block it entirely, and can be transparent or opaque, all without changing which element it is.
Other nonmetals display allotropy too, though less dramatically. Oxygen exists as the O₂ molecules you breathe and as ozone (O₃), which absorbs ultraviolet radiation in the upper atmosphere. Phosphorus has a white form that is dangerously reactive and a red form that is stable enough to coat the striking strip on a matchbox. Sulfur can form rings of eight atoms, long polymer chains, or various crystalline arrangements depending on temperature and pressure. These different structural forms give nonmetals a physical and chemical range that metals, with their more uniform metallic bonding, simply do not match.
Chemical Behavior and Bonding
The chemical properties of nonmetals flow from one central fact: their atoms hold onto electrons tightly and, when reacting, tend to gain electrons or share them rather than give them up. This electron-greediness is measured by electronegativity, and nonmetals dominate the high end of the scale. Fluorine is the most electronegative element known, and oxygen, nitrogen, and chlorine are not far behind. High electronegativity is what drives nonmetals to form two very different kinds of bonds depending on what they are reacting with.
When a nonmetal reacts with a metal, the electronegativity difference is usually large enough that the metal essentially hands over one or more electrons, producing an ionic compound. Table salt is the classic case: sodium, a metal, gives an electron to chlorine, a nonmetal, producing Na⁺ and Cl⁻ ions that lock into a crystal lattice. When two nonmetals react with each other, neither is willing to give up electrons entirely, so they share them in covalent bonds. Water, carbon dioxide, ammonia, and methane are all covalent molecules formed entirely from nonmetals.
Covalent bonding is what allows nonmetals to build the enormous variety of molecular structures found in chemistry. Carbon can form four covalent bonds at once, nitrogen three, oxygen two, and hydrogen one, and these bonding capacities combine to produce everything from simple diatomic gases to proteins containing thousands of atoms. The versatility of covalent bonding is also why organic chemistry, which is essentially the chemistry of carbon and its nonmetal partners, is such a vast field.
Reactivity Patterns Across the Group
Not all nonmetals are equally reactive, and the differences matter in practical terms. The halogens, which include fluorine, chlorine, bromine, and iodine, are among the most reactive elements on the periodic table. Fluorine is so reactive that it attacks nearly every substance it contacts, including materials that resist most other chemicals. Chlorine is reactive enough to be used as a disinfectant in water treatment precisely because it destroys organic molecules on contact. Reactivity among the halogens drops as you move down the group: bromine is less aggressive than chlorine, and iodine is milder still.
Oxygen is highly reactive too, but in a less dramatic way. It reacts with most metals and many nonmetals over time (rusting iron, tarnishing copper), and it drives combustion, the rapid reaction that powers fires and internal combustion engines. Nitrogen, by contrast, is surprisingly unreactive under normal conditions despite being a nonmetal. The two atoms in an N₂ molecule are held together by a very strong triple bond, making nitrogen gas inert enough to use as a protective atmosphere in food packaging and welding.
At the far end of the reactivity spectrum sit the noble gases: helium, neon, argon, krypton, xenon, and radon. These elements have completely filled outer electron shells, so they have no chemical motivation to bond with anything. For decades they were considered entirely inert, and they were actually called “inert gases” until chemists in the 1960s forced xenon to form compounds with fluorine under extreme conditions. Those xenon fluorides remain laboratory curiosities; in any everyday context the noble gases do not react.
Acidic Oxides and Reactions with Water
When nonmetals burn in oxygen, they generally produce acidic oxides, a chemical behavior that sets them apart from metals, which tend to produce basic oxides. Sulfur burning in air produces sulfur dioxide, which dissolves in water to form sulfurous acid. This is the reaction behind acid rain: sulfur released by burning fossil fuels reacts with atmospheric moisture and falls as dilute acid that damages buildings, acidifies lakes, and harms forests. Similarly, carbon dioxide dissolving in water produces carbonic acid, the mildly acidic compound responsible for the slight tang in carbonated drinks and for the ongoing acidification of the oceans as atmospheric CO₂ levels rise.
Nitrogen oxides follow the same pattern. When nitrogen and oxygen combine at high temperatures inside car engines and power plants, the resulting nitrogen oxides react with water vapor to form nitric acid, another contributor to acid rain. Phosphorus oxides dissolve readily in water to produce phosphoric acid, which in dilute form is the tangy ingredient in some soft drinks.
This tendency to form acidic oxides contrasts sharply with metals. Sodium oxide dissolves in water to produce sodium hydroxide, a strong base. Calcium oxide (quickite) reacts with water to form calcium hydroxide, also a base. The acid-base divide between nonmetal oxides and metal oxides is one of the most consistent chemical differences between the two groups.
Nonmetals as the Building Blocks of Life
Despite being a minority of elements on the periodic table, nonmetals make up the vast majority of living matter by mass. Living systems are built primarily from six bulk elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur, supplemented by a handful of metal ions like calcium, potassium, and magnesium.2PubMed Central. The elements of life: A biocentric tour of the periodic table Those six nonmetals form the backbone of every major class of biological molecule.
Carbon serves as the structural scaffold of all organic molecules, forming the chains and rings on which carbohydrates, lipids, proteins, and nucleic acids are built. Its ability to form four stable covalent bonds with a wide range of partners gives it an unmatched capacity for structural diversity. Hydrogen bonds, which form when hydrogen atoms bonded to electronegative atoms like oxygen or nitrogen interact with other electronegative atoms nearby, are critical for holding proteins in their three-dimensional shapes and keeping the two strands of DNA wound together. Oxygen drives the energy-harvesting process of aerobic respiration, where cells use it to produce ATP. Nitrogen shows up in every amino acid and every nucleotide, making it indispensable for both protein structure and genetic information storage.3Metals, Materials and International. The Role of Non-Metals in Biology: Essential Elements for Life
Phosphorus and sulfur round out the core six. Phosphorus is a key part of ATP, the molecule cells use as an energy currency, and it forms the sugar-phosphate backbone of DNA and RNA. Sulfur appears in two of the twenty standard amino acids, methionine and cysteine, and the disulfide bridges formed by cysteine residues help lock proteins into their functional shapes. Without these six nonmetals, the chemistry of life as we know it could not exist.
Nonmetals in Industry and Catalysis
Beyond biology, nonmetals play enormous roles in industrial chemistry. Chlorine is used on a massive scale in water purification, plastics manufacturing (polyvinyl chloride), and pharmaceutical synthesis. Sulfuric acid, derived from sulfur, is one of the most produced industrial chemicals worldwide, used in fertilizer production, petroleum refining, and metal processing. Nitrogen, extracted from the atmosphere by fractional distillation, is the feedstock for ammonia synthesis, which in turn feeds the global fertilizer industry and underpins modern agriculture.
A less obvious but growing area is the use of nonmetal-based catalysts in chemical manufacturing. Traditionally, catalysts in industrial processes have been metals like platinum, palladium, or iron. But nonmetal compounds, including certain ketones, imines, and nitroxyl radicals, have attracted attention because they resist self-oxidation and work well under mild, even aqueous conditions. Some chiral ketone catalysts derived from sugars have achieved very high selectivity in producing one mirror-image form of a molecule over another, and nitroxyl-radical catalysts can drive alcohol oxidation using cheap oxidants like sodium hypochlorite at very low catalyst loadings.4Chemical Reviews. Synthetic applications of nonmetal catalysts for homogeneous oxidations These catalysts are cheaper than precious metals and often more environmentally benign, which makes them attractive for large-scale pharmaceutical and fine-chemical manufacturing.
Silicon, which sits right on the boundary between nonmetals and metalloids, deserves a mention even though its classification is debated. Whether you call it a metalloid or a nonmetal, its semiconductor properties underpin the entire modern electronics industry. Its oxide, silicon dioxide, is the main ingredient in glass. The nonmetal-metalloid boundary is fuzzy precisely because elements near it share properties of both groups, and silicon is the most commercially important example.
What Happens to Nonmetals Under Extreme Pressure
One of the more fascinating frontiers in nonmetal science is the question of whether nonmetals can be forced to behave like metals under extreme conditions. Hydrogen, the lightest and simplest element, has been predicted for decades to become metallic at sufficiently high pressures.5Advanced Functional Materials. Metallization of Hydrogen Under High Pressure: Challenges and Experimental Progress The idea is that enough pressure would force hydrogen atoms so close together that their electrons would delocalize and flow freely, just as electrons do in a metal. If this transition occurs, metallic hydrogen could potentially be a room-temperature superconductor, which would have revolutionary implications for energy transmission and storage.
Achieving the pressures needed, estimated in the hundreds of gigapascals range, has proven extraordinarily difficult. Researchers typically use diamond anvil cells, devices that squeeze a tiny sample between two diamond tips, to reach these pressures. Several teams have claimed to observe metallic hydrogen, but the results have been contested, and reproducing them remains a challenge. Oxygen, sulfur, and iodine have all been metallized at high pressures in laboratory settings, confirming that the metal-nonmetal divide is not absolute but depends on conditions. Under the pressures found deep inside gas giant planets like Jupiter, hydrogen almost certainly exists in a metallic state, contributing to those planets’ powerful magnetic fields.
Common Misconceptions About Nonmetals
The biggest misconception about nonmetals is that they are a tidy, uniform group with properties that neatly oppose those of metals. In reality, nonmetals are far more diverse than metals. Metals share a common bonding mechanism, metallic bonding, that gives most of them similar luster, conductivity, and malleability. Nonmetals have no equivalent unifying bond type. They include monoatomic gases that do nothing chemically, diatomic gases that sustain life, volatile liquids, soft waxy solids, and the hardest natural material known. Trying to describe “a typical nonmetal” is a bit like trying to describe a typical vehicle by averaging a bicycle with a cargo ship.
Another common misunderstanding is that nonmetals are always poor conductors. Graphite conducts electricity well enough to serve as an electrode. Selenium is photosensitive and was once used in light-sensing devices. Iodine, a nonmetal solid, shows a faint metallic luster and modest conductivity. These exceptions do not reclassify the elements as metals, but they blur the line and remind you that element classification involves trends and tendencies rather than rigid walls.
People also tend to assume that reactivity is a simple spectrum running from nonreactive to highly reactive, with nonmetals clustering at one end. In practice, nonmetals span the entire range. Fluorine is the most reactive element of any kind. The noble gases are the least reactive elements of any kind. Oxygen, nitrogen, carbon, and the halogens fall at different points in between, and their reactivity depends heavily on what they are reacting with and under what conditions. Nitrogen is practically inert at room temperature but becomes dramatically reactive when heated with the right catalyst, which is exactly how the Haber process produces ammonia from atmospheric nitrogen on an industrial scale.