In practice , the transfer of electrons will always cause a change in oxidation number , but there are many reactions that are classed as `` redox '' even though no electron transfer occurs -LRB- such as those involving covalent bonds -RRB- .

In practice , the transfer of electrons will always cause a change in oxidation number , but there are many reactions which are classed as `` redox '' even though no electron transfer occurs -LRB- such as those involving covalent bonds -RRB- .
