Binary compounds – chemical substances made from just two chemical elements – are individually structurally simple, yet taken together the materials possess & exhibit a rich set of behaviours. The logical structure & reactivity arguments put forward in the Chemogenesis web book employ binary compounds as examples wherever possible.
Definition of Binary Compound
However, in this web book we use a slightly different, tighter and local – within Chemogenesis – definition:
Binary compounds are materials/substances that exhibit only one type of strong chemical bond: metallic, ionic or covalent. We are interested in the sub-set of binary compounds that are: mono bond typed.
Water, H–O–H, only has hydrogen-to-oxygen bonds, whereas hydrogen peroxide, H–O–O–H, has hydrogen-to-oxygen and oxygen-to-oxygen bonds.
Indeed, many binary compounds fail our strict one-type-of-strong-chemical-bond requirement. For example, there are literally thousands of hydrocarbons (substances consisting of hydrogen and carbon only) including: methylene, CH2, methane, CH4, ethane, C2H6, ethene, C2H4, ethyne (acetylene), C2H2, benzene, C6H6,toluene, C7H8, polythene, [CH2]n, etc.
But only methylene, CH2, and methane, CH4, possess only one type of strong chemical bond, and so are the only substances to be considered binaries, here.
Likewise, NO and NO2 are mono bond type binaries, whereas N2O3, N2O4 (the dimer of NO2) and N2O5are not.
The chemical elements as material substances are here – within the Chemogenesis web book – considered to be special case binaries where the two elements are identical: H2, O2, N2, F2, Cl2, Br2, I2, P4, S8, etc.
This definition also holds with bulk elemental materials: lithium, Li, carbon as diamond, carbon as graphite, silicon, Si, etc. that exist as extended lattice structures rather than forming discrete molecules.
It transpires – as will be discussed over the next few pages of this web book – that there are 4 general classes of mono-bond typed material, elemental and binary: metallic, molecular, network covalent and ionic. These can be naturally arranged into a truncated tetrahedron of bond type: