Oxygen and its unexpected neighbours
Ask a chemistry student who oxygen's relatives are and they will point straight down the periodic table: sulfur, selenium, tellurium, polonium. That is oxygen's column, group 16, the chalcogens.
Ask a set of physical measurements the same question and you get a different family.
We took ten physical properties for all 118 elements and asked which elements look most like oxygen across all ten at once. Sulfur and selenium make the list. Tellurium does not, and neither does polonium. Oxygen's closest company turns out to be a cluster of light gases and nonmetals drawn from five different columns of the table.
The cohort
In order, oxygen's ten nearest neighbours are nitrogen, fluorine, chlorine, hydrogen, sulfur, krypton, bromine, argon, phosphorus and selenium.
The top three are almost tied. On a scale where 1 means two elements point in exactly the same direction, nitrogen scores 0.995 and fluorine 0.993. Chlorine follows at 0.976. The tenth place, selenium, still scores 0.827. Helium narrowly misses the cut in eleventh. Tellurium, oxygen's own column-mate, sits back in 17th at 0.57, and polonium is far down the list at 0.05.
Why does the table's vertical logic come apart? The groups of the periodic table organise elements by how they behave chemically. Our measurements describe what the elements are physically like: how cold they melt and boil, how dense they are, how strongly they attract electrons, and how big their atoms are.
Judged that way, oxygen is a small atom that is still a gas far below room temperature. In the source data it melts at 54.36 K and boils at 90.19 K, and its Pauling electronegativity of 3.44 is one of the highest anywhere. Nitrogen (boiling at 77.36 K) and fluorine (85.03 K, electronegativity 3.98) share that profile almost exactly. Chlorine, krypton and argon are gases too. The cohort spans the halogens (fluorine, chlorine, bromine), the noble gases (krypton, argon), nitrogen and phosphorus from group 15, and hydrogen on its own in group 1.
The neighbourhood is not uniform, though. Sulfur, phosphorus and selenium are solids at standard conditions, and bromine is a liquid. They still score highly on the remaining measures, such as electronegativity and atomic size, although this comparison does not isolate which feature contributes most to any individual score. Selenium boils at 958 K, more than ten times oxygen's figure, yet it still lands in the top ten.
Neighbours of neighbours
A single list can be a fluke of one element's numbers, so we checked who sits closest to oxygen's two nearest neighbours.
Nitrogen's and fluorine's cohorts are almost copies of oxygen's. Ten elements appear in all three groups, counting each element itself: hydrogen, nitrogen, oxygen, fluorine, phosphorus, sulfur, chlorine, argon, bromine and krypton. Together the three groups contain only twelve distinct elements. The two extras are helium and selenium.
The closeness runs both ways. All ten of oxygen's neighbours also list oxygen in their own top ten. That is not automatic: each element gets its own cut-off, so a strong mutual score can still fall outside one element's top ten. Oxygen also turns up in the neighbourhoods of fifteen different elements, against a typical figure of ten. In this data it is something of a hub for the light nonmetals and gases.
How the comparison works
Every element is described by ten numbers: melting point, boiling point, density (on a log scale), molar heat capacity, Pauling electronegativity and five measures of atomic radius. Each property is rescaled so that no unit dominates, and similarity is the cosine of the angle between two elements' profiles. Five of the ten measures are radii. They are correlated with one another, so atomic size can carry extra weight, but that does not mean it decides any particular score. Each feature's actual contribution varies by element.
Gaps matter too. Where a value is missing, we fill it with the typical value across all elements, and those fills are not measurements. Metallic radius is missing for all eleven elements in this cohort, and molar heat for seven of them. Shared stand-ins make the members look somewhat more alike than the measured data alone would show. A high score here describes resemblance in these numbers, not interchangeable chemistry.
The point
None of this overturns the periodic table. Groups remain the best guide to how elements react. What the matrix offers is a second view, one that ignores the columns and asks only what an element is physically like.
From that angle, oxygen's company is not the chalcogen column. It is a crowd of small, light, mostly gaseous elements, the air you breathe and its near relations, gathered from five different groups.
Data: Bowserinator/Periodic-Table-JSON (https://github.com/Bowserinator/Periodic-Table-JSON), largely derived from Wikipedia (https://en.wikipedia.org/wiki/Oxygen and linked element pages), licensed CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0/). Data snapshot retrieved 8 November 2026. Similarity analysis by The Elements.