Relativistic effects are known to play a fundamental role in determining the properties of gold, even imparting it with a yellow color. Here we use ab initio calculations and an evolving theory that allows the electron charge density to be partitioned into chemically meaningful structures to show that these effects also give rise to gold's well-known resistance to oxidation by making oxygen insoluble in gold. We go on to show that silver, despite having the same lattice constant and oxygen binding energy as gold, is extremely susceptible to oxidation because the relativistic effects in silver are smaller than in gold. (c) 2013 Elsevier B.V. All rights reserved.