List of alternative nonmetal classes
| Metalloid | Unclassified nonmetal | Nonmetal halogen | Noble gas |
| B, Si, Ge, As, Sb, Te, Po, At | H, C, N, P, O, S, Se | F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
| Polycrystalline β-boron chunks | Liquid oxygen in a glass beaker | Liquid bromine in a jar | A krypton-filled discharge tube glowing bluish-white |
In chemistry, after nonmetallic elements such as silicon, chlorine, and helium are classed as either metalloids, halogens, or noble gases, the remaining unclassified nonmetallic elements are hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and selenium.
The nonmetallic elements are sometimes instead divided into two to seven alternative classes or sets according to, for example, electronegativity; the relative homogeneity of the halogens; molecular structure; the peculiar nature of hydrogen; the corrosive nature of oxygen and the halogens; their respective groups; and variations thereupon.
Classification science
Classes provided an economy of description and are beneficial to structuring knowledge and understanding of science. The distinction between classes is not absolute. Boundary overlaps can occur as outlying elements in each class show or begin to show less-distinct, hybrid-like, or atypical properties. As expressed by Nelson:Two classes
| Reactive nonmetal | Noble gas |
| H, C, N, P, O, S, Se, F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
Rudakiya. The nonmetals are simply classified according to their inclination to form chemical compounds. The halogens are not distinguished.
Three classes
Wulfsberg. The nonmetals are divided based on a loose correlation between electronegativity and oxidizing power. Very electronegative nonmetals have electronegativity values over 2.8; electronegative nonmetals have values of 1.9 to 2.8.| Other nonmetal | Halogen | Noble gas |
| H, C, N, P, O, S, Se | F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
Bettelheim et al. The nonmetals are distinguished based on the molecular structures of their most thermodynamically stable forms in ambient conditions. Polyatomic nonmetals form structures or molecules in which each atom has two or three nearest neighbours ; diatomic nonmetals form molecules in which each atom has one nearest neighbour ; and the monatomic noble gases exist as isolated atoms with no fixed nearest neighbour. This gradual reduction in the number of nearest neighbours corresponds to a reduction in metallic character. A similar progression is seem among the metals. Metallic bonding tends to involve close-packed centrosymmetric structures with a high number of nearest neighbours. Post-transition metals and metalloids, sandwiched between the true metals and the nonmetals, tend to have more complex structures with an intermediate number of nearest neighbours
Four classes
Field & Gray. Hydrogen is placed by itself on account of it being "so different from all other elements". The remaining nonmetals are divided into nonmetals, halogens, and noble gases, with the unnamed class being distinguished by including nonmetals with relatively strong interatomic bonding, and the metalloids being effectively treated as a third super-class alongside metals and nonmetals.| Hydrogen | Carbon and other nonmetals | Halogen | Noble gas |
| H | C, N, P, O, S, Se | F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
Dinwiddle. A variant of Field & Gray in which carbon, nitrogen, oxygen, phosphorus, sulfur, and selenium are classified as carbon and other nonmetals.
| Metalloid | Intermediate nonmetal | Corrosive nonmetal | Noble gas |
| B, Si, Ge, As, Sb, Te | H, C, N, P, S, Se | O, F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
Vernon. The nonmetals are divided into four classes that complement a four-fold division of the metals, with the noble metals treated as a subset of the transition metals. The metalloids are treated as chemically weak nonmetals, in a manner analogous to their chemically weak frontier metal counterparts.
Five classes
Dupasquier. Noble gases were not known in 1844 when this classification arrangement was published. Hydrogen, carbon, nitrogen and oxygen were grouped together on account of their occurrence in living things. Phosphorus, sulfur and selenium were characterised as being solid; volatile at an average temperature between 100 degrees and red heat; and combustible and flammable.| Hydrogen | Semiconductor | Other nonmetal | Halogen | Noble gas |
| H | B, Si, Ge, As, Sb, Te | C, N, P, O, S, Se | F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
Myers et al. Metalloids are labeled as semiconductors and carbon, nitrogen, oxygen, phosphorus, sulfur, selenium as other nonmetals.
| Hydrogen | Metalloid | Nonmetal | Halogen | Noble gas |
| H | B, Si, Ge, As, Sb, Te, Po | C, N, P, O, S, Se | F, Cl, Br, I | He, Ne, Ar, Kr, Xe, Rn |
Dingle. Hydrogen is again placed by itself on account of its uniqueness. The remaining nonmetals are divided into metalloids, nonmetals,, halogens, and noble gases. Since the metalloids abut the post-transition or "poor" metals, they might be renamed as "poor non-metals".