Jan Arnold Albert Ketelaar (21 April 1908, Amsterdam – 23 November 2001, Lochem)[1][2] was a Dutch chemist and author of the textbook Chemical Constitution: an Introduction to the Theory of the Chemical Bond (De chemische binding. Inleiding in de theoretische chemie).[3][4] Van Arkel–Ketelaar triangles are named after him.[5]
Ketelaar's doctoral students included Sol Kimel and Robert de Levie.[6][7] He was elected a member of the Royal Netherlands Academy of Arts and Sciences in 1958.[1]