  The bonding pattern of a covalent semiconductor is disrupted when a surface
is cut while keeping a rigid (truncated bulk) geometry. The covalent bonds are
partly reformed (with a sizeable energy gain) when reconstruction is allowed.
We show that the ``electron localization function'' (ELF)---applied within a
first--principles pseudopotential framework---provides un unprecedented insight
into the bonding mechanisms. In the unreconstructed surface one detects a
partly metallic character, which disappears upon reconstruction. In the surface
reformed bonds, the ELF sharply visualizes strongly paired electrons, similar
in character to those of the bulk bonds.
