The Cl2 molecules in crystalline chlorine are arranged in herringbone arrays within sheets, held together by covalent bonds. The shortest Cl to Cl distance within these sheets is 1.98 Ao. Adjacent sheets are held together by van der Waals' forces and the closest approach between Cl atoms on neighboring sheets is 3 .69 Ao. In solid HCI observed at lower temperatures, the H-Cl bond length is 1.25 Ao. Therefore shortest distance between two Cl atoms in solid HCI is (given van der Waals' radius of H =1.1Ao):