And so for TWO hydrogen atoms, two #dotH# radicals, the electrons couple to form a covalent bond; conceived to be a region of HIGH electron density between 2 adjacent nuclei such that electrostatic repulsion between the positively charged nuclei is NEGATED, and a net attractive force results.
On the other hand, #"ionic bonding"# results from the transfer of electrons between (typically) a metal, and a non-metal to form discrete anions, #X^-#, and cations, #M^+#, which are bound together in a non-molecular array by strong electrostatic forces. In the melt (or in solution) the ionic bond is disrupted and the ions are free to carry a current under these conditions - of course these conditions require high temperature, or dissolution in a polar solvent.
In the former case, where covalent bonding operates in a discrete molecule, there are no free electrons or ions to carry a current, because of the molecularity of the material, and the absence of free electrons.
