Soldering terminology

A type of bond where two atoms share a pair of electrons. To indicate this, one simple C-H bond or the C-C double bond is often written as C:H and C :: C. For this reason, the term electron pair bond is in use. Multiple covalent bonds reduce the distance between the atoms and more energy is required to break these bonds. The illustration shows the electron pair bonds of ethane (C₂ H₆) and ethylene (C₂ H₄). The former has a single covalent bond (2 electrons), the latter has two (4 electrons). At a distance of the carbon atoms of 1.3 Å (angstroms), the binding is tighter than the ethylene in the ethane (1.5 Å distance), and thus more stable.

The bond has even more stability if the electrons in the pair have an opposite spin. The thermal fission energy acting on an organic fluxing agent during soldering is relatively low because the process takes place at a rather low temperature. Therefore, the presence of covalent bonds and the number of electron pairs must be considered when choosing the flux activator.