Hydrogen is a chemical element with an atomic number of 1. It has just one proton and one electron. Deuterium is the heavier naturally occurring, non-radioactive, stable isotope of hydrogen. Deuterium was discovered by Harold Urey in 1931, for which he received the Nobel Prize in 1934. The deuterium isotope effect has become an important tool in the  elucidation of the mechanism of chemical reactions. Deuterium contains one proton, one electron, and a neutron, effectively doubling the mass of the deuterium isotope without changing its properties significantly. However, the C–D bond is a bit shorter, and it has reduced electronic polarizability and less hyperconjugative stabilization of adjacent bonds, including developing an anti-bonding orbital as part of the newly formed bond. This can potentially result in weaker van der Waals stabilization, and  can produce other changes in properties that are difficult to predict, including changes in the intramolecular volume and the transition state volume. Substituting deuterium for hydrogen yields deuterated compounds that are similar in size and shape to hydrogen-based compounds.