text: diagonal relationship? can anyone explain the diagonal-relationship between b and si??? thx million this is best understood in terms of them both being on the borderline between metals and non-metals - in particular, the fact that their oxides are acidic. boron is quite different to silicon in respect of the fact that its simple covalent compounds are electron-deficient, that is they only have six electrons in the outer level. thus they are strong lewis acids. silicon can accept electron pairs, but only by expanding its valency octet.