PETER W. ATKINS is a Professor of Chemistry at Oxford University, UK, a fellow of Lincoln College, and the author of more than fifty books for students and a general audience. His Physical Chemistry broke new ground by stressing understanding over memorization. Now in its Eighth edition, it remains the leading text in its field. LORETTA JONES is a Professor at the University of Northern Colorado, USA. Loretta's speciality is chemical education; she is currently Chair of the Division of Chemical Education of the American Chemical Society.