Properties of water equal to that of the hydrogen ion (), which gives a pH of 7 at 25 °C. Action of water on rock over long periods of time typically leads to weathering and water erosion, physical processes that convert solid rocks and minerals into soil and sediment, but under some conditions chemical reactions with water occur as well, resulting in metasomatism or mineral hydration, a type of chemical alteration of a rock which produces clay minerals. It also occurs when Portland cement hardens. Water ice can form clathrate compounds, known as clathrate hydrates, with a variety of small molecules that can
Descriptor (chemistry) the arrangement of atoms, usually of carbon atoms in carbon skelets. "n", "iso" and "neo" are no longer used in the systematic nomenclature, but still frequently in trivial names and in laboratory jargon. The prefix "n" describes a straight-chain carbon skeleton without branches, whereas "iso" describes a branched skeleton, without specifying any further details. More generally, "iso" is a compound which is isomeric to the "n" compound (a compound in which individual atoms or atomic groups are rearranged) "neo" is a non-specific term for "new", usually synthetically produced substances or isomers of long-known "n" compounds or natural substances (for example