Noble gases do have electronegativity, but pinning down reliable values for them has been one of the more stubborn problems in theoretical chemistry. The difficulty is practical: electronegativity scales like Pauling’s were built around how atoms behave in chemical bonds, and noble gases rarely form bonds under ordinary conditions. That left their cells blank on many textbook charts, giving generations of students the impression that electronegativity simply does not apply to helium, neon, argon, and their neighbors. More recent computational work has filled in those blanks, and the results are surprising enough to reshape how chemists think about this entire group of elements.
Why the Pauling Scale Leaves Noble Gases Blank
Linus Pauling’s electronegativity scale, the one most people encounter first, is derived from bond energies. You compare the energy of a bond between two different atoms to the average energy of the bonds each atom forms with itself, and the difference tells you how unevenly the bonding electrons are shared. The catch is obvious: if an element does not form enough bonds for you to measure, you cannot slot it into the scale. When Pauling published his values, noble gas chemistry barely existed. Xenon difluoride would not be synthesized until 1962, and argon and neon compounds were decades further away. So the noble gases were simply omitted.
Some later researchers tried to fill in the gap by extrapolating from periodic trends. If electronegativity rises across a period as you move from metals toward halogens, you might expect it to keep rising one more step to the noble gas at the end of each row. That reasoning gave noble gases the highest electronegativities in their respective periods, sometimes even higher than fluorine’s. These extrapolated values appeared in some reference tables and created a persistent misconception: that noble gases are inert because they hold onto their electrons so tightly that no other atom can pull charge away from them. The reality, as computational chemistry has since shown, is more nuanced.
Where Noble Gases Actually Land on a Consistent Scale
A 2015 study tackled the problem head-on using the Mulliken definition of electronegativity, which is based on two measurable quantities: how much energy it takes to remove an electron from an atom (ionization energy) and how much energy is released when the atom gains one (electron affinity). The challenge with noble gases is that the second ingredient is tricky. Noble gas anions are unstable, so their electron affinities cannot be measured the way you would measure, say, chlorine’s. Instead, the researchers used carefully chosen computational methods to estimate those values.
The resulting scale overturned the old extrapolation-based picture in three important ways. First, noble gas electronegativity decreases steadily as you move down the group, from helium to radon, just as it does for halogens and most other families. Second, the highest electronegativities in each period belong to the halogens, not the noble gases. And third, noble gas values fall close to those of the chalcogens, the group that includes oxygen, sulfur, and selenium.1PubMed. The noble gases: how their electronegativity and hardness determines their chemistry That last point is striking: it means xenon’s electronegativity is in the same neighborhood as sulfur’s, not off in some extreme corner of the periodic table.
This matters because it reframes the story about why noble gases are unreactive. The old narrative, that they have sky-high electronegativities and cling to their electrons with unmatched ferocity, was always a bit circular. The updated picture says noble gases have moderate electronegativities and are unreactive for a different reason, one tied to their electronic hardness.
Hardness and Why Moderate Electronegativity Does Not Mean Easy Bonding
Alongside their electronegativity values, the same study computed the chemical hardness of noble gases. Hardness, in this context, measures how resistant an atom’s electron cloud is to being rearranged by an outside influence. A “hard” atom does not easily shift its electron density toward a bonding partner; a “soft” one does. Noble gases turned out to be, by a wide margin, the hardest elements on the periodic table, and this hardness decreases as you go from helium down to radon.1PubMed. The noble gases: how their electronegativity and hardness determines their chemistry
This combination explains a lot. Having a moderate electronegativity means a noble gas atom is not uniquely greedy for electrons. But having extreme hardness means it resists the electron-density distortions that bonding requires. The heavier you go down the group, the softer the noble gas becomes, and the easier it is to coax into forming bonds. That lines up perfectly with the experimental record: xenon chemistry is well established, krypton forms a handful of compounds, argon has a few exotic molecules, and helium and neon are almost impossible to bond under normal conditions.
The Noble Gas Compounds That Exist
If electronegativity values are real and measurable for noble gases, you would expect at least some of them to form bonds. They do, and the list has been growing since Neil Bartlett first demonstrated a xenon compound in 1962. Xenon difluoride, xenon tetrafluoride, and xenon hexafluoride are all well-characterized, stable enough to study at room temperature, and commercially available as chemical reagents. Krypton difluoride is less stable but real. These compounds typically pair the noble gas with fluorine or oxygen, the two most electronegative elements, because those are the atoms with enough pull to overcome the noble gas’s resistance to sharing electrons.
Lighter noble gases require more extreme conditions. Argon fluorohydride (HArF) was first made and characterized by trapping argon atoms in a frozen matrix with hydrogen fluoride and hitting them with ultraviolet light. Computational studies of this molecule found it has an unusually large response to electric fields along its axis, a consequence of the dramatic electronic rearrangement involved in getting argon to participate in bonding at all.2PubMed Central. The dipole moment, polarizabilities, and first hyperpolarizabilities of HArF. A computational and comparative study The molecule exists, but only under cryogenic conditions. It is not something you would find sitting in a flask on a shelf.
Even further down the difficulty ladder, argon has been found bonded to hydrogen in space. Argonium (ArH⁺) was detected in the Crab Nebula and other interstellar regions, a discovery that caught many chemists off guard. Follow-up work has identified other potential noble gas cations in interstellar and computational contexts, including ArOH⁺, NeOH⁺, and ArNH⁺.3PubMed Central. Formation of Potential Interstellar Noble Gas Molecules in Gas and Adsorbed Phases All of these are cationic species, meaning the noble gas atom has effectively been turned into an electron acceptor by having its electron count reduced, which gets around the hardness problem.
Aerogen Bonding, a Noncovalent Surprise
One of the more unexpected developments in noble gas chemistry is the discovery that covalently bonded noble gas atoms can participate in noncovalent interactions with electron-rich partners. When a noble gas like xenon is bonded to highly electronegative atoms such as fluorine, its electron density gets pulled unevenly, creating a region of positive electrostatic potential on the opposite side of the atom. That positive region can attract lone pairs from nearby Lewis bases or anions, forming what researchers have named an “aerogen bond.”4PubMed. Aerogen Bonding Interaction: A New Supramolecular Force?
This is analogous to halogen bonding or chalcogen bonding, where similar positive electrostatic regions on bonded halogens or chalcogens attract negative partners. Aerogen bonding has been documented both computationally and experimentally in crystal structures of xenon fluorides, where the arrangement of molecules in the solid state cannot be explained without these interactions.5PubMed Central. Covalent and Non-covalent Noble Gas Bonding Interactions in XeF (n) Derivatives (n = 2-6): A Combined Theoretical and ICSD Analysis The existence of aerogen bonding depends directly on the electronegativity of the noble gas: the interaction arises because the noble gas has enough electronegativity to participate in polar covalent bonds, but not so much that its electron density cannot be distorted by its bonding partners.
Oganesson, the Noble Gas That Might Be a Metal
Element 118, oganesson, sits at the bottom of the noble gas column and pushes the trend lines to their limits. A 2021 study that computed thermochemical electronegativities across the periodic table found oganesson’s value to be strikingly low, around 2.59, placing it in the same range as lead rather than near its noble gas relatives.6Nature Communications. Thermochemical electronegativities of the elements The cause is relativistic effects. In superheavy elements, inner-shell electrons move at a significant fraction of the speed of light, which changes the shape and energy of all the atom’s orbitals. For oganesson, these effects are strong enough to blur the clean separation between filled and empty orbitals that gives lighter noble gases their stability.
The practical upshot is that oganesson is predicted to behave less like a noble gas and more like a reactive, possibly metallic element. Only a few atoms of it have ever been synthesized, and they decayed in milliseconds, so direct chemical experiments are not feasible. But the theoretical prediction is consistent across multiple research groups: the monotonic decrease in noble gas electronegativity going down the group, combined with intensifying relativistic effects, eventually produces an element that defies the category it nominally belongs to. If oganesson could be made in bulk, its chemistry would likely have very little in common with neon or argon.
Helium Under Extreme Pressure
At the opposite end of the group, helium is the hardest atom to coax into any kind of bonding. Its electron affinity is essentially zero, its ionization energy is the highest of any element, and its tiny electron cloud gives bonding partners almost nothing to work with. Under normal conditions, helium chemistry is nonexistent in any practical sense.
But “normal conditions” is doing a lot of work in that sentence. A 2025 computational study explored what happens when helium is mixed with fluorine at pressures in the range of millions of atmospheres, the kind of pressure found deep inside giant planets and white dwarf stars. The simulations predicted a stable compound, He₃F₂, in which helium’s 1s electrons participate in genuine polar covalent bonds with fluorine. Analysis of the electronic structure showed that at these extreme pressures, the energy gap between helium’s occupied and unoccupied orbitals shrinks enough for fluorine’s orbitals to mix in, forming He–F bonds that would be unthinkable at atmospheric pressure.7PubMed. Chemical Bonding between Helium and Fluorine under Pressure
This result has not been confirmed experimentally, because generating and maintaining multi-terapascal pressures in a lab while also characterizing the product is beyond current capabilities. But it illustrates a broader point about electronegativity and noble gas chemistry: the values are not fixed properties of isolated atoms in a vacuum. They describe tendencies, and those tendencies can be overridden when conditions are extreme enough. Helium has electronegativity. It just takes astonishing force to make that electronegativity relevant.
Why Textbooks Still Get This Wrong
The blank cells in electronegativity charts persist partly from inertia and partly because there is no single universally accepted set of noble gas values to fill them with. The Pauling scale genuinely cannot accommodate elements that do not form enough bonds for its energy-difference method. The Mulliken-based scale can accommodate them, but it requires careful computational treatment of unstable anions, and different research groups using slightly different methods arrive at slightly different numbers. The Allen spectroscopic scale, which defines electronegativity as the average energy of valence electrons in a free atom, can also handle noble gases in principle, since it depends only on spectroscopic data and does not require the atom to form bonds.8American Chemical Society (ACS Publications). Electronegativity is the average one-electron energy of the valence-shell electrons in ground-state free atoms
The result is a patchwork. Some scales give noble gases the highest values in their period. Others place them more modestly, near the chalcogens. The Mulliken-based results make the strongest case that the “noble gases on top” picture is an artifact of extrapolation rather than a measured reality, and that a self-consistent computational approach places halogens firmly at the top.1PubMed. The noble gases: how their electronegativity and hardness determines their chemistry But until a single scale achieves the kind of consensus that the Pauling scale enjoys for maingroup elements, textbooks tend to punt on the issue entirely.
For students, the practical takeaway is that a blank cell does not mean “no electronegativity.” It means “we have not agreed on the best way to measure it.” Noble gases attract electron density in bonds. They form compounds. They participate in noncovalent interactions. They have electronegativity values that fit coherently into the periodic trends of their neighbors. The blanks in the chart are a limitation of the chart, not of the elements.
Noble Gas Chemistry in the Cosmos
One place where noble gas electronegativity matters in a surprisingly tangible way is astrophysics. The detection of ArH⁺ in the interstellar medium was not just a curiosity; it gave astronomers a new diagnostic tool. Because argonium forms preferentially in regions with very low molecular hydrogen density, its spectral signature acts as a marker for diffuse atomic gas. The molecule exists because ionized argon has enough electron-accepting character to grab a hydrogen atom and hold on, at least until something knocks the molecule apart.3PubMed Central. Formation of Potential Interstellar Noble Gas Molecules in Gas and Adsorbed Phases
Researchers have since used computational methods to explore whether other noble gas cations could exist in interstellar conditions. Candidates like NeOH⁺ and ArNH⁺ are thermodynamically plausible and could, in principle, be detected with sufficiently sensitive radio telescopes. These molecules are vanishingly rare and short-lived by terrestrial standards, but in the vast, dilute environment of space, even fleeting species accumulate enough to leave spectral fingerprints. The electronegativity of the noble gas atom, modest as it may be, is what makes the bond possible in the first place. Without it, these ions would not hold together long enough to emit or absorb at characteristic frequencies, and astronomers would lose a useful window into the chemistry of the cosmos.