a. Chem. [f. TRI- + ATOM + -IC.] a. Having three atoms in the molecule. † b. = TRIVALENT. Obs. c. Containing three hydroxyl groups (OH); = TRIHYDRIC a.1
1862. Miller, Elem. Chem. (ed. 2), III. 53. To the triatomic group [of elements] belong nitrogen, phosphorus, arsenic, antimony, bismuth, and gold.
1863–72. Watts, Dict. Chem., I. 464. To classify them [primary hydrides and chlorides] in four principal groups, thus: Monatomic, Diatomic, Triatomic, Tetratomic. Ibid. (1872), VI. 237. Nitrogen, which combines with 3 atoms of hydrogen, is triatomic, triadic, or trivalent.
1882. Roscoe, Elem. Chem., xxxv. 320. The possible number of derivatives of the triatomic alcohols is much larger than that of either of the preceding classes.
1894. Times, 18 Aug., 10/3. No doubt the passage of … the diatomic form of the substance to the triatomic form … takes place with evolution of heat.
1903. Edin. Rev., Oct., 393. It [radium] can ozonise oxygen—that is, condense it by rendering its molecules tri-atomic.
