A set of rules for predicting the structure of a cluster compound based in the number of electrons in the framework counted in a particular way. The electrons counted are known as skeletal electrons. The rules apply to polyhedra that have triangular faces (known as deltahedra). They were originally applied to the boron hydrides. Electron pairs in bonding between two boron atoms are counted as skeletal electrons but the pairs in B-H units are ignored. However, if a boron atom is connected to two hydrogens (BH2), the second bond is counted with the skeletal electrons. According to the rules, if the formula is [BnHn]2− and there are n+1 skeletal electron pairs, then the structure is closo. If the formula is BnHn+4 and these are n+2 skeletal electron pairs, the structure is nido. If the formula is BnHn+6 and these are n+3 skeletal electron pairs, the structure is arachno. The rules are named after the British chemist Kenneth Wade, who first formulated them in the early 1970s.