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.
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