Formula unit Formula unit A formula unit in chemistry is the empirical formula of any ionic or covalent network solid compound used as an independent entity for stoichiometric calculations. It is the lowest whole number ratio of ions represented in an ionic compound. Examples include ionic NaCl and KO and covalent networks such as SiO and C (as diamond or graphite). Ionic compounds do not exist as individual molecules; a formula unit thus indicates the lowest reduced ratio of ions in the compound. A "chemical formula" shows the kinds and numbers of atoms in the smallest representative unit of a substance. In
Common minnow Hamilton. According to the selfish herd theory, a group forms as individuals try to reduce their domain of danger by approaching others and continuously moving toward the center of the group where the risk of predation is the lowest. As the theory predicts, common minnows increase their shoaling behavior in response to increased predation pressure. Common minnows can detect the predators’ presence and communicate with their shoalmates by a chemical signal that is detected by olfactory nerves. The chemical, named Schreckstoff after a German word meaning "fear substance" by Karl von Frisch who first described it, is contained in specialized