After the relevant nonmetals are classified as either noble gases or halogens, the remainder are considered on a group-by-group basis. Since the metalloids abut the post-transition or 'poor' metals, they might be renamed as 'poor non-metals'. The remaining nonmetals are divided into metalloids, nonmetals, (referred to as 'quintessential nonmetals'), halogens, and noble gases. Hydrogen is again placed by itself on account of its uniqueness. Metalloids are labeled as semiconductors and carbon, nitrogen, oxygen, phosphorus, sulfur, selenium as other nonmetals. 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, carbon, nitrogen and oxygen were grouped together on account of their occurrence in living things. Noble gases were not known in 1844 when this classification arrangement was published. The metalloids are treated as chemically weak nonmetals, in a manner analogous to their chemically weak frontier metal counterparts. 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. A variant of Field & Gray in which carbon, nitrogen, oxygen, phosphorus, sulfur, and selenium are classified as carbon and other nonmetals. 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.ĭinwiddle. Hydrogen is placed by itself on account of it being 'so different from all other elements'. 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 neighboursįield & Gray. Metallic bonding tends to involve close-packed centrosymmetric structures with a high number of nearest neighbours. A similar progression is seem among the metals. This gradual reduction in the number of nearest neighbours corresponds (approximately) to a reduction in metallic character. Polyatomic nonmetals form structures or molecules in which each atom has two or three nearest neighbours (carbon: C x phosphorus: P 4 sulfur: S 8 selenium: Se x) diatomic nonmetals form molecules in which each atom has one nearest neighbour (hydrogen: H 2 nitrogen: N 2 oxygen: O 2 fluorine: F 2 chlorine: Cl 2 bromine: Br 2 iodine: I 2) and the monatomic noble gases exist as isolated atoms (helium, neon, argon, krypton, xenon, radon) with no fixed nearest neighbour. The nonmetals are distinguished based on the molecular structures of their most thermodynamically stable forms in ambient conditions. Very electronegative nonmetals have electronegativity values over 2.8 electronegative nonmetals have values of 1.9 to 2.8. The nonmetals are divided based on a loose correlation between electronegativity and oxidizing power.

The nonmetals are simply classified according to their inclination to form chemical compounds.

Provided that this is done, however, it constitutes a very useful classification, and although purists often despise it because of its approximate nature, the fact is that practising chemists make a great deal of use of it, if only subconsciously, in thinking of the chemistry of different elements.' Two classes Įxamples have author labels for convenience, rather than precedence Reactive nonmetal As expressed by Nelson: '…care needs to be taken to remember that… is only an approximation, and can only be used as a rough guide to the properties of the elements. Boundary overlaps can occur as outlying elements in each class show or begin to show less-distinct, hybrid-like, or atypical properties. The distinction between classes is not absolute. The nonmetallic elements are sometimes instead divided into two to six (or 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.Ĭlasses provided an economy of description and are beneficial to structuring knowledge and understanding of science. In chemistry, after nonmetallic elements such as silicon, chlorine, and helium are classed as either metalloids, halogens, or noble gases, the remaining unclassified elements are hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and selenium.

As element metal or nonmetal